Aspis Prison was one of the game's original arenas. It's the smallest arena, with only 10 tiles.

Super Feature

In-game description: TRESPASSERS WILL BE PUNISHED AFTER THE RISING MAGMA AWAKENS THE UNDEAD WARDEN.

Details:

The magma reaches the lowest tile about 40 seconds after the start of the game
The magma starts to rise 20 seconds after the start of the game
The magma deals 20 damage per second to a player who stands in it
The Warden appears one minute after the start of the game
The Warden's projectiles deal 10 damage from a direct hit
The Warden fires one projectile every 25 seconds
There's no way to kill The Warden. Once he appears, he stays until the end of the game

Trivia

Aspis Prison is the only arena that loses one of its tile over the course of the game, which happens when the lava rises above the lowest tile
Aspis is also the only arena with a tile that moves (the elevator tile)
The developers were very deliberate when designing the elevator to minimize the risk of motion sickness when standing on it
You used to be able to see the sky through the bars on the Prison's ceiling, but now it's blocked