An artistic level is full of beautiful (or not) pictures to look at. Usually, there is no goal, but sometimes there are minigames, though. A lot of times, the editors of the world place gravity dots that connect with each art creation.
Sometimes, there are bosses, so the creator can keep the players busy in the level.
There are two types of art levels: full art, and pixel art. Full art levels are one entire, detailed picture, usually original and improvised. Pixel art worlds contain very small art scattered throughout the level, often copied directly off of Smilies or video game sprites.
Art levels take time to make, but, if the right kind of art is made, then players will get interested in the art, raising the level's popularity, and usually paying off all the effort the owner has spent making the art.