Cranial City is the hub of the Caliosteo Islands, and has many deserts and volcanic areas. It is also home to Joe Wildwest, Caliosteo Park's Owner, Lester, and Pauleen. The Dig Sites are Mt. Krakanak, Dusty Dunes, and Rainbow Canyon.
Ilium Village is very cold and has lots of snow. Its dig sites have many Water type Vivosaurs, and you can find Rupert, Cole, and Princess Pooch there. The Dig Sites are Hot Spring Heights, Icegrip Plateau, and Bonehemoth.
The Barebones Base and ZongaZonga's Castle are not islands, but are accessible.
The BareBones Base is home to the BareBones Brigade. You can Challenge Robo-Don Post-Game.ZongaZonga's Castle is where the final Boss is, and Post-Game, you can revisit it to relive the battle.