Cactus is an hilariously competitive multi-player game where humans run around in a feeble attempt to catch the elusive flying cacti (plural for cactus). There are two teams: Catchers, and Cacti. Each team has it's own classes and there are plenty of twists and turns in the game play. Objectives are simple: Humans catch as many cacti as they can, and cacti try to escape the humans (perhaps kill a few if necessary).
As you can see, the map is constructed to look like a glass cage. The cacti are meant to fly high, so I found that making an illusion of a confined, yet spacious environment would make the game make more sense (if that's even possible).