The ideal site for a sauna is near a freshwater river, where river rocks are plentiful. A planned escape path to cool down in the river or bay is also nice, the closer the better.

You will also need a fire pit that adheres to low-impact standards to heat the rocks. Building a fire below the high tide line will minimize impact. It should be within 40 feet of the sauna tent, but no closer than 15 feet, so any sparks from the fire do not land on the nylon materials. The fire needs to be medium sized (closer to a campground-sized fire, than a backpacker-sized fire), and you will need to select wood for its ability to produce heat and coals, not sparks. Choose dry downed wood. While cedar is commonly found as driftwood, it's not the best choice, since it throws sparks.

To build a sauna, I use the following materials: a full-coverage rain fly (all sides extend to the ground) from a six-person tent (I use a Sierra Designs six-person Mondo Condo, but most winter mountaineering tents have full-coverage rain flys); a set of folding tent poles (you can order a replacement fly and poles from many tent manufacturers); and a tarp to place over the sauna in case it rains.

At home, before the trip, I shortened each of the three tent poles by one section. I then added small pieces of Velcro along the seams in the fly to secure the poles to the fly, and sewed short webbing strips with grommets to secure the end of each pole. I also placed one grommet in the center of the rain fly, to allow excess steam to vent.

To construct the sauna, I set up the fly without the tent. When I set up the revised fly, it looks like a squatty tent.

Arranging sitting benches inside will add to the comfort. Collect the sleeping bags from everyone on the trip, then connect them from the hang loops at the foot ends with a carabiner or cord, and drape them over the fly for insulation. Construction is now complete.