Onsen are hot springs, also used to refer to the bathing facilities around the hot springs. In contrast, sentou are indoor public bath houses where the baths are filled with gas-heated tap water. Beppu has eight major hot springs known as “Beppu Hatto” (Beppu Eight). Beppu has the second-largest amount of hot spring water discharge in the world, with 2,909 vents.
My study abroad program was in the summer, through the tsuyu rainy season and on into the sweltering humidity of June-July. Some days, even fresh from a shower, it only took thirty seconds to be dripping with sweat again. It was the worst season for hot baths. Regardless, I had come across the Pacific Ocean to Japan’s most famous onsen locale; I wasn’t going to leave without trying a few.
One of my favorite onsen experiences was at Kitahama Hot Spings, Termas. Termas has an outdoor bath the size of a small swimming pool. Because it was co-ed, we wore swimsuits; a good thing, because the multistory hotel between the bathhouse and the bay had lots of overlooking windows. I would definitely have raised an objection to traveling businessmen surveying a women’s bath from their hotel suites.
It was hard to resist floating around despite the no-swimming rule. There are several standard onsen rules, such as no swimming, splashing or noisiness (don’t disturb the other patrons), don’t drop your towel in, and (this might disappoint a lot of foreign visitors) anyone with a tattoo cannot enter the bath. I suppose this is to deter yakuza (mafia) from hanging out and scaring customers.
With the breeze from the bay, warm water to soak in and surrounding city lights, visiting Termas was one of the most surreal and wonderful nights I spent in Beppu. I’m sad that, because I didn’t want to get my camera wet, I couldn’t take any pictures.
To make up for it, here’s a very cute illustrated article on onsen rules: http://www.wattention.com/archives/onsen/
 Wikipedia contributors. “Onsen.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 18 Aug. 2014. Web. 6 Oct. 2014.
 Wikipedia contributors. “Beppu Onsen.” Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 8 Jan. 2014. Web. 6 Oct. 2014.