According to Wikipedia, Enryaku-ji was founded in 788, torched and burned to the ground at some point, and then rebuilt in the 16th and 17th centuries. It’s the headquarters of the Tendai Buddhist sect which originally came to Japan from China. To me, those names, magnetsu and manten, just sound like poetic names for women (magnetsu) and men (manten). My impression is that Japanese people have traditionally separated the place where they bathe from the place where they use the toilet. There seem to be so many words for bathroom. (furoba, otearai, basuruumu, etc.) Enryaku-ji is very old and has been mainly a place where Buddihist monks have lived. The Western idea of “bathroom” is probably quite new in Japan. My knowledge of kanji is currently quite limited but I love to do zen meditation so I do know something about Buddhism.