Lindsey C.
Yelp
I have been to a lot of onsen and sento in the past. This place, though missing a lot of bells and whistles of newer onsen, is so neat inside that it's definitely worth visiting. The building itself is a huge, beautiful, Meiji era (I think?) styled old building with a ton of history. You often have to line up and wait to get in, but they told us 45 minutes and it ended up being less than 10.
The place is packed with people coming in and out constantly. You pay to go in (but if you're staying in the area, ask at the desk of your hotel, because they may be able to sell you a discount ticket there) and you go inside, lock up your shoes and then go on into the locker room, where you get undressed.
The actual dressing and bath rooms are also super old school, and when I went the bath tub was absolutely PACKED with people, the whole outside wall of the bath surrounded with people enjoying the water.
When you get out and get dressed again, it's fun to enjoy a cold milk in a glass bottle near the shoes area, or if it's later in the day, you can enjoy a frosty cold beer from the nearby Dogo Brewery right outside the door.
Anyway, if you're in the area there are a lot of good baths, and some good open-air baths too, but this place is worth a trip for the historical architecture alone.