Bowser's Highway Showdown, also known as World 1-Castle, is the final standard course of World 1 in Super Mario 3D World. It is a Castle with many Kick Bombs, with Bowser serving as the boss. The Green Sprixie Princess is held prisoner in the castle. It is unlocked by completing Plessie's Plunging Falls or Switch Scramble Circus. Ten Green Stars are needed to enter and its own completion the Green Sprixie Princess who builds a Clear Pipe to World 2.