Bowser's Castle is where most of the final battles with Bowser take place. Super Mario Bros. marked the first appearance of Bowser's Castle. Here, a fortress was at the end of every world, until the last which was Bowser's Castle. It appeared again in Super Mario Bros. 3, where it was in the Dark Land. It appeared a third time in Super Mario World, where there was a big sign that said Bowser was right outside of it. The castle also has a secret back door that allows you to fight Bowser much sooner instead of going through all of the sections of the castle. Bowser's Castle was then adopted into being a race track in the Mario Kart series.