Refers to the natural geothermal water itself, or the source. Often used in compound words like 温泉街 (hot spring town) or 温泉卵 (hot spring egg).
この地域にはたくさんの温泉が湧いている。
Many hot springs bubble up in this area.
温泉の成分が肌にいいらしい。
The minerals in the hot spring water are said to be good for the skin.
onsen; hot spring resort; hot spring spa
Refers to a bathing facility or resort town built around a hot spring. Often implies a place with public baths, inns, and a relaxing atmosphere.
週末に温泉に行ってゆっくりしたい。
I want to go to a hot spring resort and relax this weekend.
あの温泉は露天風呂が有名だ。
That onsen is famous for its open-air bath.
I bathed in the inn's hot spring before going to sleep.
I'm planning to go to a hot spring resort with my family this weekend.
I soaked in the open-air hot spring and gazed at the mountains.
Last autumn, I stayed overnight at a hot spring resort in Hakone.
I want to go on a hot spring tour after I retire.
A hot spring gushes out at the foot of this mountain.
新しい旅館のために温泉を掘った。
They drilled a hot spring well for the new inn.
温泉 specifically means a natural hot spring, while 湯 more broadly covers any hot bath or hot water, including a home bath.
hot spring area; hot spring district
hot spring resort; spa town