People can no longer live on Earth. It needs to regenerate. The whole mankind moved to a different galaxy consisting of eleven planet. When the last ship was about to colonize the last planet of the system, there was unexpected crash that caused the crystal - the important source of energy - to fall into several pieces.

Poseidon: Planet Eleven mixes platforming gameplay with light puzzle-solving. The player guides the astronaut through the underground caves in order to collect pieces of a broken crystal. Survival depends on two elements: energy of the hero and fuel to his jetpack. When the first runs out, the hero dies and depletes the player one of three lives. When the second runs out, the hero is unable to jump higher which is crucial in order to collect crystals and proceed further. There are many obstacles on the way: passive - doors which need to be opened by keys - and active - enemies spawning in random places throughout the whole room. All the enemies can be killed with the gun but only some of them are really in the range. The aim of the game is to collect all the crystal pieces and bring them to the bottom of the cave to the place where they could be joined together.