Kaiju Alpha Islands

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You choose a spawn island from the map selector that appears after you pick a kaiju.

The five islands

IslandShapeBuildingsWhat it is likeBest for
Tokyo U-shaped, with a large bridge joining the two arms Very dense, most of it destructible The most visited island in the game, and the least peaceful. Expect a fight the moment you land. Cell and XP farming on buildings — if you can survive the traffic
Isla De Mara Volcano plus a large city Substantial city block Big enough that fights tend to cluster in one area and the rest stays quiet Farming with an escape route. It also holds the game's tallest terrain.
San Francisco Two islands joined by a large bridge Moderate Not especially popular, which is exactly why some players use it Roleplay and staged fights on the bridge
Forest Grassy island ringed by tall dirt walls None — the only island with no man-made structures The quiet one. Most players never go. Levelling in peace: the trees can be destroyed for cells and XP just like buildings
Thailand Small Few Unpopular because of the lack of space Destroying things without being interrupted

Picking an island for what you are actually doing

Farming cells: the trade is density against interruption. Tokyo has the highest ceiling per minute and the highest chance that a bigger kaiju ends your run; the Forest has a lower ceiling and almost no risk. Isla De Mara sits between the two — a real city block, but big enough that the fighting concentrates in one area you can simply avoid. Routes are on the cell farming page.

Hunting Monster Zero skulls: only one skull exists per server, so you are sweeping and rejoining rather than fighting. Small quiet islands are searched faster and interrupted less; Tokyo's building density works against you here, because geometry is exactly what hides a world object. See the skull page.

Roleplay and staged fights: San Francisco's bridge is the reason that island has a following despite being unpopular for farming.

Secret Arena Island

How to find it: Follow the directional sign on the volcano island.

What is there: A large open battlefield with a central throne, two massive insectoid statues facing the arena, and two smaller statues at the entrance.

What it does: None known. The community wiki records no gameplay mechanic attached to it, and it is variously read as an easter egg, a testing area, or a teaser for something unreleased. We have not found a developer statement either way.

Worth being precise about the wording: "no known purpose" is not the same as "nothing there". The arena is real and reachable. What nobody has produced is a mechanic attached to it, and until someone does, calling it a boss arena or an upcoming game mode is a guess.

How current is this

Island pages on the community wiki. These are among the wiki's older pages — the roster has changed far more since than the map has, but treat descriptive detail as dated rather than certain.