The Training Island
The Training Island is the Island where Master Roshi takes his students to train because his smaller island is not enough to have his students train. Roshi has his house transported by Capsule from his small isolated one to this island. Goku and Krillin spent alot of time doing "training" like delivering milk across the whole island, moving dirt, swimming, dodging bee's and school work. The Island is very big and populated with many people living in a village on it. Their is a jungle with many animals living in it where Roshi through the rock for Goku and Krillin to find. As comic relief in the milk delivery part it shows them carrying milk in several different climates such as desert, arctic and others. It is unknown if the island really does have those features or if it is just comic relief. This island is also the battle site of Yamcha and Tambourine in an anime filler of the King Piccolo Saga.
In Dragon Ball Advanced Adventure The Training Island is featured as a side scrolling stage reenacting the hunt between Goku & Krillin for the rock with Roshi's signature on it.