Let’s see . . . the Baha’i facility in Chicago (back when I was a Baha’i), a synagogue in Indianapolis (as a paid musician, for a music festival), and a several mosques in Istanbul Washington, D.C., Damascus, and Cairo. The most impressive was Cairo’s al-Azhar Mosque. In the middle of an absolutely filthy city, the al-Azhar was so clean you could eat off the floor.
Edit: Oh, and a number of Shinto shrines, when we were living in Japan.