For general purposes, this book is probably only a 4. But for my purposes, for my interest in the history of bathing, hygiene, and especially steam/sweat baths, it's a 5. It's not just a history/background book, but I like it for that (though I feel, since it's from 1978, that one should try to cross-check his material to see if research has uncovered more or different information). On the other hand, for those who are interested in bathing and especially sweat bathing, just reading it and browsing through the pictures is a pleasure.
I've already read a great deal of this book online, since the author put segments online when the book went out of print (unfortunately, the out-of-print price for this title is about $150, or I'd already have bought one): http://www.cyberbohemia.com/Pages/swe... The short section in the printed book on "Bathing in Medieval Europe" (from 1978) is not reproduced online; it has several illustrations that I've seen elsewhere but never been able to track down the source... which appears to be, based on Aaland's citations (thank you thank you Mr. Aaland!) to be this book: https://archive.org/details/deutsches...
Aaland spent 3 years visiting and photographing sweat bathing customs, including Islamic (specifically Turkish) hammam, Finnish Sauna, Russian Banya, Japanese sweat baths, and native American sweat lodes. He also includes history on bathing around the Mediterranean (Roman/Greek and the Islamic hammam), small sections on Bathing in medieval Europe, alleged historical Irish hot air bathing, and some reports of hot air/vapour bathing in "Tribal Africa" (as the author mentions on his website, the book was written in 1978; the "Tribal Africa" section was one he wisely did not put online, as it's light on information and unfortunately thick in colonialist word choices.
What I find especially interesting are the sections not just on Russian and Finnish sweat bathing, but on sweat bathing as it was practiced in the pre-conquest Americas. I had no idea there were Maya sweat baths, and I'd always been confused by the similarities between sweat lodge traditions among Native American tribes as reported by rainbow-sparkle types... but Aaland writes clearly about non-Sioux (aka other than Black Elk's books) sweat lodge customs and fits them in with the context of the other customs of sweating he's described.
Unlike many authors writing about the history of bathing, Aaland does give a bibliography, even if he doesn't cite his references directly, and as I noted above, he gives illustration credits for his illustrations, both of which are helpful to someone with an interest in the subject.
Aaland also set out to give instructions for building sweat baths/saunas at home in this book; I admit to not being handy enough to make use of them. The copy I borrowed through ILL has had pages 221-226 torn out (A Tent Sauna, A Trail Sweat, A Private Sweat bathing cubicle), along with p. 233-34. If one is interested in more up-to-date versions of this content, I'd suggest you pursue the ebook that Aaland is selling online of his booklet, How to Build Your Own Sauna and Sweathttp://www.cyberbohemia.com/Pages/bui...