Where Can You Do a Cold Plunge in Marathon Florida?
Updated: 4 days ago
Harmony Point at Grassy Flats, on the westernmost end of the property right on the beach, has three four-person cold plunges. They run between 40 and 55 degrees and are set next to a beautiful, twelve-person wood-fired sauna.
You don’t have to be a hotel guest. It’s $35 per person for an hour. If you’re staying at Grassy Flats, it’s already in your resort fee.
That’s the short answer. Marathon is a small town, and this is the only place in it built for this. The rest of this page is what the session actually looks like, what the water is kept at, and how to do it right.
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1. Is there a Public COld Plunge in Marathon Florida?
Yes, one. Harmony Point at Grassy Flats, and it’s open to anyone, not just hotel guests.
That’s worth being straight about. Marathon has about 8,000 people. It doesn’t have a recovery studio scene and it isn’t going to. What it has is a resort that built three real cold plunges and a wood-fired sauna on the beach, then opened them to the public by the hour.
So if you’re picturing a storefront with a front desk, a locker room and a membership tier, that doesn’t exist here. What you get instead is a landscaped deck on the westernmost point of the property, open air, water on three sides. Book an hour, show up, get in.
2. Do you have to be a hotel guest to use the cold plunge at Grassy Flats?
No. Anyone can book it.
Grassy Flats sells Harmony Point by the hour to the public, same as it does to guests. You book a slot, you show up, you use the sauna and the plunges for your hour. $35 a person.
If you are staying at Grassy Flats, it’s already covered in your resort fee. Nothing extra to pay, you just book your hour like everyone else.
There’s a cap, which is the part worth planning around. Twelve people per hour, across one sauna and three tubs. That’s deliberate. It’s the number that keeps the sauna from being shoulder to shoulder and keeps you from waiting on a tub. It also means the hour you want can be gone, especially in season and especially at the end of the day when everyone comes off the water at once.
Book ahead if you have a specific time in mind. If you’re flexible, mid-morning is the easiest slot to get.
3. Where is Harmony Point?
Harmony Point is the westernmost end of the Grassy Flats property, out on the beach past the rooms. Grassy Flats sits at mile marker 59 on the ocean side of the Overseas Highway, in Grassy Key at the top end of Marathon. Mile 59 lands you a little past the halfway point, close enough to the Seven Mile Bridge to see it on your way in.
The point itself got its name before any of this was built. John Denny, who was one of the first people to bring paddle boards to the Keys, has been running a small meditation out there for years. The sauna and the plunges went in around that rather than replacing it.
4. How Cold is the Cold Plunge?
Between 40 and 55 degrees, depending on which tub you get in.
There are three of them, four people each, and they’re staged on purpose. One runs around 55. One around 50. One sits at 40 to 45.
That staging matters more than it sounds. Most places have one tub at one temperature, which means the number was picked for somebody else. Here you pick. If it’s your first time, 55 is cold enough to do everything cold is supposed to do and you’ll actually last three minutes in it. If you plunge at home and 50 stopped registering a while ago, the cold tub is there.
The tubs come from EMRJ, built by John Kleener at Live Water Sports. He’s been shaping paddle boards in the Keys for years and roto-molds the plunges in the same factory, which is a strange sentence until you’ve seen how much the two things have in common. Four-person tubs, built to sit outside in the Keys year round, with shade cloths over them. The shade is for the equipment, not for you.
5. Is there a sauna next to the cold plunge?
Yes. A twelve-person wood-fired sauna, out on the beach, with the plunges tucked in behind it.
It runs between 170 and 190 degrees, dry. That range isn’t arbitrary. Dry heat in the high 170s is where the cardiovascular work actually happens, which is the difference between a sauna and a hot room.
It can also run cooler. Drop it to 120 or 140, add water and aromatherapy, and you get a steam session with more humidity and more sweat. It feels harder. It does less for your heart rate. Both are worth doing, they’re just not the same thing, and it’s worth knowing which one you’re in.
Wood-fired means someone is tending it, and it means the temperature moves. If the room gets hotter than you want, the fix is burping the sauna, which is opening it up for a minute and letting some heat out. If you want it hotter, that’s a conversation with whoever’s running the session, not a thermostat.
Twelve people fit. Three four-person tubs sit behind it. The whole thing is set into a landscaped deck on the point, open air, water on three sides.
6. Is the Cold plunge water actually clean?
It’s filtered continuously, with no chlorine or chemicals, to a standard that clears Florida pool code.
A cold plunge is a small volume of water that a lot of people get into, one after another, all day, immediately after sweating hard. The math on that is not great, and most places running a plunge have not solved it. A tub of ice in the corner of a gym gets drained when someone remembers.
John Kleener built a multi-stage filtration system for these using hydrogen peroxide instead of chlorine. It runs constantly rather than between sessions, and it was engineered to exceed what the Department of Health requires for a commercial pool, which is the standard these fall under.
The other half of it is a rule. You shower after the sauna, before you get in the water. Every time, no exceptions. Outdoor showers are right there. It takes twenty seconds and it’s the single biggest thing that keeps the water clean, which is why it isn’t optional.
7. What else is at Harmony Point besides the cold plunge?
An outdoor Fitness Area, a few steps from the tubs.
It’s not a fitness room. There’s no mirror and no machines. Pull-up bars, monkey bars, a dip rack, a bench, kettlebells, dumbbells and assault bikes, all of it built to live outside in salt air. Primitive tools for the kind of movement that carries over to the water.
That’s Matt Sexton’s bias showing, and he’s open about it. He spent a career as a professional waterman without ever really being a gym guy, and his problem with conventional strength training is that too much of it makes him worse at the things he actually wants to do outside. So what went in here is what keeps you moving, not what makes you bigger.
You get it with the same hour. Sauna, plunges, Fitness area, it’s all one booking and one price, and you use the hour however you want it. Some people lift and then plunge. Some people plunge and then lift. Nobody will tell you which.
There’s more on the program itself on the gym page.
8. How Long Should You Stay in a Cold Plunge?
Three minutes.
That’s the number worth aiming at. Long enough for the cold to do what it does, short enough that it’s a realistic target rather than a test of will.
The first thirty seconds are the worst of it. Your breath goes shallow and fast and everything in you says get out. If you can slow your breathing down and hold it there, the next two and a half minutes are more manageable than the first thirty seconds suggest. Most people who quit, quit in the first minute.
If three is out of reach today, get in anyway. A minute of actual cold beats five minutes of water you’re comfortable in, and the tub at 55 exists so you have somewhere to build from.
The part people skip is what happens after. When you get out, stay out for three minutes before you go back to the heat. That’s not recovery time, that’s the point of the exercise, and there’s more on why in the protocol below.
9. What is the Right Sauna and Cold PLunge Protocol?
Twelve to fifteen minutes in the sauna. Three minutes in the plunge. Three minutes out, breathing. Repeat three times. That’s the hour.
Here’s what each piece is doing.
The sauna, twelve to fifteen minutes. Dry, 170 to 190. By around minute thirteen most people are running a heart rate in the 150s or 160s, which is the range you’d hit on a hard ride. You are sitting still while that happens, which is the strange part and the appealing part.
The plunge, three minutes. Heart rate comes down fast, sometimes into the high 50s or 60s. The swing between those two numbers inside of a few seconds is the work.
Three minutes out, which is the part everybody skips. You get out of the cold tub and you do not get back in the heat. You stand there, you breathe, and you let your body figure out how to warm itself up. That’s the whole point. Rewarming on your own is where the real response happens, and walking straight back into a 180 degree room skips it entirely.
Then go again. Three rounds fits in an hour with time to spare.
You’re not required to do any of this. You get the hour and you use it how you want, and the written recommendation is posted out there if you want to follow it. What’s above is just what the people who built it would tell you to do.
A few times a year there are guided sessions with breath work, run as retreats rather than a daily thing. If you want someone talking you through it rather than a card on the wall, that’s the version to look for.
10. Do You Do the Cold Plunge Alone or is it Guided?
Mostly on your own. You book the hour, you get the space, and the recommended routine is posted if you want to follow it. There’s supervision out there, because it’s a wood-fired sauna and someone has to tend it, but nobody is running you through a session.
A few times a year that changes. There are guided retreats with breath work, where someone walks the group through the whole thing start to finish. Those are scheduled events, not something on the daily menu.
What’s worth knowing either way is that you probably aren’t doing this alone.
Twelve people share the hour. Three tubs, four to a tub. So the three people getting in the cold water with you are the three people who were just sitting next to you in the sauna for fifteen minutes, sweating, talking about whatever people talk about in a sauna.
That changes minute two considerably. Alone in a cold tub, minute two is where you negotiate with yourself and usually lose. In a tub with three other people who are all visibly having the same bad time and nobody’s moving, you stay. Most groups make it to three together. Not because anyone’s competitive about it, just because getting out first is somehow harder than staying in.
If you want the tub to yourself, book an off hour and you’ll probably get it. Most people find they’d rather not.
11: Is a Cold Plunge Worth it Somewhere this Warm?
The Keys are hot and the water is bath temperature most of the year. That’s exactly why a 40 degree tub does something the ocean can’t.
Shock is the mechanism. Not cold, shock. Your body needs a sharp enough gap between where it is and where it suddenly finds itself to trigger a response, and swimming in 85 degree water doesn’t come close. Neither does a cool shower. The gap has to be big, and the only way to get a big gap in a place like this is to build one.
Which is also why the sauna sits ten feet away. Going from 180 to 45 in the space of a few steps is a bigger swing than you’d get anywhere outdoors in the Keys at any point in the year.
Then there’s what people actually do here. A day of kiting is six hours of bracing against a kite with your whole body, and you don’t notice what it costs until the next morning when your shoulders won’t open and your core has opinions. Same with a long day on a foil, or poling a skiff, or anything else that looks like standing still and isn’t.
That soreness is the thing the cold is for. Sitting in 45 degree water for three minutes won’t undo a hard day, but the people who do it after one generally report the next morning going better than it otherwise would have. That’s the honest version of the claim.
There’s also the weather case, which is less noble and completely real. It’s August, it’s 94 degrees with the humidity, and you’ve been outside since seven. Getting into cold water for three minutes is the best you will feel all day.
12: How Much Does A Cold Plunge Cost in Marathon?
$35 per person for an hour. That’s sauna, all three plunges and the outdoor fitness area, and it’s the same hour whether you use all of it or sit in the sauna the whole time.
If you’re staying at Grassy Flats, it’s covered by your resort fee. You still book an hour, you just don’t pay for it again.
There’s a day pass if you want more than the hour. It runs $75 to $100 and adds use of the resort for the day along with paddle boards and kayaks, with your hour at Harmony Point included in it. That’s the one that makes sense if you’re driving in from somewhere else in the Keys and want to make the trip worth it rather than turning around after sixty minutes.
What’s not included: drinks and anything from the market. You can bring your own water bottle. Everything else is sold on property.
13: How Do You Book a Cold PLunge Session?
Book an hour, pick a time, show up. Twelve people per hour across the sauna and three tubs, so slots are finite and the good ones go first.
Hotel guests book the same way, it’s just already paid for in the resort fee.
Worth booking ahead rather than turning up, especially in season. Late afternoon is the hardest slot to get, because that’s when everyone who’s been on the water all day comes in wanting the same thing at the same time. If your schedule is flexible, you’ll have an easier time earlier.
Day pass is a separate booking, since it covers resort access and watersports alongside your hour at Harmony Point.
What to expect when you arrive: outdoor showers are right there, there’s a waiver to sign, and you’ll want a swimsuit and a towel. Full list of what to know is further down.
14: What Do You Need to Know Before Your First Session?
Shower between the sauna and the plunge. Every round, no exceptions. Outdoor showers are a few steps away and it takes twenty seconds. This is the rule that keeps the water clean.
There’s a waiver. Standard, signed once.
Don’t drink before. Alcohol and cold water and 180 degree heat are a bad combination, and that’s not a house preference, it’s the reason the rule exists.
Don’t do this pregnant. Not the sauna, not the plunge.
Bring a swimsuit. Towels are provided. Everything else you’d want is sold at the market.
You can bring your own water bottle. No other outside food or drink, which is a property-wide
rule rather than anything specific to Harmony Point. Drink more water than you think you need, before and after.
If you’ve got a heart condition, are on medication that affects your blood pressure, or you’re not sure how your body handles heat, talk to your doctor before you book. That’s not us covering ourselves. Fifteen minutes at 180 degrees followed by three minutes at 45 is a real cardiovascular event and it should be a deliberate one.
First time, give yourself the 55 degree tub and permission to get out early. Nobody’s watching the clock but you.
15: Who Should Not Book This?
This isn’t a spa. If what you want is a treatment room, a massage, a robe and a quiet room with cucumber water, book somewhere that does that. There’s no in-house masseuse at Grassy Flats and nobody’s pretending otherwise. Harmony Point is an outdoor deck with a wood fire, three cold tubs and a pull-up bar on it.
It’s also not private. Twelve people share the hour. If the idea of sitting in a sauna with strangers for fifteen minutes sounds like the opposite of relaxing, that’s a reasonable thing to know about yourself, and this is the wrong booking.
It’s outside, and it’s the Keys. There’s shade over the tubs and landscaping around the deck, but you’re in the weather. In August that means you’re hot before you start. In a January front it means the walk between the sauna and the tub is its own event.
And if you’re looking for a guided wellness experience with an instructor talking you through every phase, that’s a few times a year, not a Tuesday. Most days it’s a card on the wall and your own judgment.
What this is for: you’ve been on the water, you’re wrecked, and you want the fastest route to feeling human again. Or you plunge at home and you’d like to keep doing it on vacation. Or you’re driving the Keys, you’ve been in a car for two hours, and the idea of a sauna and a cold tub on a beach sounds better than another bar.
16: What Else Can You Do in Marathon After A Cold Plunge?
Most people don’t drive to mile 59 for an hour and leave.
If you’re already on property, the obvious one is getting on the water. Grassy Flats runs kiteboarding, wing foiling, e-foiling and paddle boards out of the same stretch of beach, and the honest order of operations is water first, plunge after. The sauna is better earned.
If you came off a charter or a long session and the plunge was the whole reason you drove down, the fitness area is ten feet away and included in your hour. Worth knowing before you book, since most people assume it’s separate.
Beyond the property, Marathon is a small town with more in it than it looks: Sombrero Beach, the Turtle Hospital, the Dolphin Research Center, and the Old Seven Mile Bridge if you want to walk out over the water. The day pass exists for exactly this kind of day, where the hour at Harmony
Point is one piece of it rather than the whole trip.
11. FAQ
What should you wear in the cold plunge?
A swimsuit. Towels aren’t provided, so bring one of those too. There are outdoor showers on the deck and you’ll be using them between rounds, so come dressed for that rather than planning to change.
Can you do a cold plunge if you’ve never done one before?
Yes, and the three tubs exist so you have somewhere to start. Take the 55 degree one, aim for a minute, and get out when you want to. The staging means you’re not choosing between the deep end and nothing.
How many people can be in the cold plunge at once?
Four to a tub, three tubs, twelve people in the hour. You won’t be waiting on a plunge, and you won’t have one to yourself either.
Is the cold plunge open year-round?
Yes. The sauna is wood-fired and the tubs are built to sit outside in the Keys through the season, so it runs the same in January as it does in July. The experience is different in August, when the walk back to the sauna is the only cold you’ll find outside the tub.
Do you need to bring your own towel?
No. Towels are provided at Harmony Point. Just ask at Check-in.
