1. Kami's Lookout - Kami's lookout floats high in the sky a few miles above Korrin's tower. On it Lives the guardian of the Earth, Kami and his assistant Mr.Popo. The Room of Spirit and Time is also located on Kami's Lookut.
Who Trainied Here? - Tien, Yamcha, Krillin, Chaozu, Yajirobe

2. Master Roshi's Island - The very small island where Master Roshi lives. He lives with his turtle and some other animals. He has a small house on the island.
Who Trained Here? - Chibi Goku, Krillin, Adult Goku (Movie 5)

3. King Kais Planet - The humble home of King Kai. His small Planet is located at the end of Snake way and has 10x more gravity than Earth. King Kai lives here with his monkey, Bubbles, and Gregory. At the end of the Cell saga, the planet is destroyed when Cell Self-Destructs.
Who Trained Here? - Goku, Piccolo, Tien, Yamcha, Chaozu