Mountain Hell (山地獄) is one of Hell Tour of Beppu Onsen, Oita Prefecture. It's a steam Onsen. The temperature of Onsen Water is about 90 degree celcuis. They use this heat to keep animals warm, so it is a zoo.
Tourist Info.
Admission: 400 Yen for adult, 300 Yen for High school, 250 Yen Junior High, 200 Yen for kids.
Time: 8:00 to 17:00
There is parking and restroom.
8 Hell pass: 2,100 Yen for adult.
There is group discount.
Access
1. at Beppu Station.
2. Use local bus 2,5,24 to Umijigoku.
400 JPY
30 min
New Wave Samurai Movie. 
映画好き集まれ！ 
Mountain Hell was named because the steam of this Onsen was just like a mountain. They use the heat of Onsen Water to breed Animals.
Animals
Hippopotamus
Snow Monkey
Flamingo
American Miniature Horse
Others.
Official web site:http://www.beppu-jigoku.com/images/English0.pdf