It is the largest in Beppu Jigoku and features a cobalt blue pond.

Umi Jigoku got its name because the color of the pond looks blue like the sea. The blue color of the pond is due to dissolved iron sulfate, a component in the hot springs. Also, the temperature of the pond is extremely high at approximately 98 degrees, which is enough to boil eggs.

Umi Jigoku is a spot where you can enjoy the charms of hell, such as footbaths and hot spring eggs. Also, from the observation deck, you can see a panoramic view of Umi Jigoku.