specialty bath; themed onsen bath
Refers to a hot spring bath where the water is infused with flowers, fruit, herbs, or other items for fragrance, color, or seasonal enjoyment. Common at ryokan and onsen facilities.
この旅館では、季節ごとに変わり湯を楽しめます。
At this ryokan, you can enjoy a different specialty bath each season.
今日の変わり湯はゆず湯です。
Today's specialty bath is a yuzu citrus bath.
Compound of 変わり (kawari, 'change' or 'unusual') and 湯 (yu, 'hot water' or 'bath'). The term likely arose in the context of onsen culture to describe baths that differ from plain hot spring water.