Princess Peach makes a special cake and invites Mario to her castle in Mushroom Kingdom. As Mario arrives, he learns that Bowser took over the castle and kidnapped Peach. To defeat Bowser and rescue Peach, Mario enters each worlds on painting walls. The main hub of the game is Peach's castle. The player can unlock doors by collecting stars. There are 120 of them scattered among 15 maps and some secret maps. The player can get each of the stars by completing each of the achievements per level. One world requires two stars, for instance. Each locked door leads to more levels and challenges. Mario can also leave the castle and explore the small courtyard.