banejo

Bani is to bathe and -ej- is the place where the root happens, so a banejo is a place for bathing. The same suffix gives lernejo a school, necesejo a toilet, preĝejo a church and kuirejo a kitchen. It is the most productive room-builder in the language.

Which place, though, depends on context, and this word straddles two. Indoors it is the bathroom. Outdoors it is the lido, the baths, the swimming spot on the river. If you need the room specifically and the sentence could go either way, banĉambro says bathroom and nothing else. And keep necesejo separate: in much of continental Europe the room with the bath and the room with the toilet are two different rooms, and Esperanto follows the continent here rather than the British house.

One more from the same root: banujo is the bathtub itself, the container, which is -uj- rather than -ej-. A place you go into, a container you sit in.