Ocean

The ocean (海洋, Kaiyō), sometimes referred to as the sea (海, Umi), is the body of water surrounding land in the Digital World such as File Island and Server Continent.

File Island
File Island is surrounded by the ocean.

Underwater Cave
The Underwater Cave (海底洞窟, Kaitei Doukutsu) is a cave located deep in the Ocean of the Digital World.