It will probably only get used during the winter. and I can see some maintenance issues too with all that moisture inside it would be easy to get mildew or mold growth started if it is not maintained properly and often. also it is traditional to follow up your time in the sauna with a dive into a nice cold lake (or pool), or at least you might want to have a cold outdoor shower nearby. personally I would spend my money on something like a hot tub before I bought a sauna.

I am in N.Central Florida near The Villages where I own rental houses .My 89 yr old mother is in a RAL nearby that has a max of 5 patients and theOwners also live in the 7 bedroom house. 

Sometimes local credit unions or banks nearby are more up for this kind of thing. 

Look for a farm credit ("FCS") institution nearby.

Also if you don't know, there is a relatively new and expanding Navy base near by, increasing active duty military demand for housing.

Using this strategy can help you save money on improvements and eventually raise the value of the house.Make connections with nearby real estate agents, go to gatherings, and make use of BiggerPockets and other educational materials.

This is why I always preach buying fewer but more desirable properties.

I think our tenants have liked having the owner nearby, in case last minute repairs or issues come up.

Establishing connections with nearby experts is crucial.5.

Often times, I will do that for free especially if I'm going to be nearby, but if they do it more than once in a short period, I will charge a fee and they aren't surprised by that either.