Actual labyrinths; only one (very long) way to the core. If constructed in the shape of a spiral, it may serve as a kind of "guided" version of bullet hell style bosses; once you enter the labyrinth, the core will fire a dense stream of bullets, and the only way to avoid them is to keep moving forward, towards the center, where one needs to promptly destroy the core, or be disintegrated.

Extra fun for the first time player: The core doesn't start firing until it's too late for the player to turn around and escape. :-)