[Deleted the ad] is the best spa in the world […] you can read more about it [Deleted the rest of the ad and the URL]
I sincerely doubt it is the best spa in the world.
In my country for instance we have several places called ‘wellness centers’ that have multiple saunas (with degrees varying from 65C to 90C). An interesting experience is the ‘pouring session‘ performed by a ‘pouring master’ (really don’t know what the english terms are), who pours water on the hot stones so the hot sauna gets moist making it even harder to be in it. These session are always held at set hours in one of the saunas on the parc. In that moisty heat the ‘master’ starts waving his/her towel at the individuals attending the session, so all of a sudden you get very hot air on your skin to which the skin reacts with goose bumps
while having it so hot you are giving ice cubes to put on your wrists/ankles.
Some people do not make it till the end of the session and leave the sauna to cool off.
Apart from the saunas every center has at least one or two huge bubblebaths, indoor and outdoor swimming pools, a hamam, a large steam room, some infrared ‘saunas’. Some saunas offer salt baths where floating is easy, or herb baths as well.
You can always sign up for some massages, or special facial/body treatments, both of which will cost you extra.
Of course, unlike your hotel no bathing suits or underwear are allowed, but some wellness centers have started to have one day in the week where a bikini or a swimming short is allowed. Of course these are the less hygienic saunas for those of us who are truly in for getting the real sauna experience (Wearing a swimming outfit you simply can not clean your self in the shower at every spot of your body after each sauna, or after going to the loo, which normally you are expected to do).
Only in the restaurants you are expected to wear a bathing gown. In the rest of the area you can walk naked, but some wear a towel around them, that is when walking from one sauna to the other of course.
To give you an idea, here are photos of just three centers:
https://www.elysium.nl/faciliteiten/
http://www.devarana.nl/_module/photo_album/5
http://www.devarana.nl/_module/photo_album/2
https://www.thermenbussloo.nl/nl/sauna/saunas/
https://www.thermenbussloo.nl/nl/sauna/baden/