also: だついしょ
noun
Specifically the area in a bathhouse, swimming pool, or similar facility where you undress before entering the bathing area. Also used for the sink/mirror area adjacent to a bathroom in a home.
温泉の脱衣所で服を脱いだ。
I took off my clothes in the changing room of the hot spring.
脱衣所の洗面台で顔を洗う。
I wash my face at the sink in the dressing area.
更衣室 is a general changing room (e.g., in a clothing store or gym), while 脱衣所 specifically implies undressing for bathing or swimming.
Compound of 脱衣 (undressing) + 所 (place).