Where there is one, there are many - quite often that is the case with onsens. This makes sense - a powerful underground source of hot water mineralized would break out in multiple spots, or at least will be accessible via boreholes in a quite large area.
Such places become onsen towns. Japanese people would normally say just 温泉 - “a hot spring”, and mean the whole area rather than a particular ryokan or bath-house. While the worlds 温泉町 exists in the language - it was hijacked by a particular town in Hyogo prefecture (they read it as おんせんちょう though) and now confuses everybody. You can also say 温泉郷 meaning the onsen village, or 温泉街 - a town or a district within a larger town, or 温泉地 with an emphasis on the area itself.
Anyways, so what’s the big deal? Imagine you are approaching an onsen town. Before you can make out individual buildings - you see clouds of steam rising over the rooftops. You enter - and there is so much hot water that it runs down the trench along the road - that’s where so much steam is coming from. Instead of central square - a pool of otherworldly color, with more steam coming out of it.
Japanese religious tradition is in close connection to forces of nature, and of course volcanic fire pushing steaming water out of the earth’s crust is one of them. You will find shrines and temples dedicated to worshipping hot water and forces behind it in onsen towns, and see rituals and practices which you would not find in any other place.
Some onsen towns and villages are maintained to preserve as much historic ambiance as possible. You will find cobblestone roads, wooden buildings, traditional shops selling old-fashioned sweets and souvenirs. I suggest you bring your kimono with you to blend in 😉.
Some other onsen towns are mixed more organically with everyday life. Take for example Beppu - a modern city with universities, museums and stadiums, and own airport. And a multitude of hot spring hotels. Get to the one with bath on the rooftop and enjoy the city view while relaxing in healing hot water.