Crystal Caves, or World D, is the fourth secret world of Newer Super Mario Bros. Wii. It is unlocked by completing the secret exit in World 5-8: Magma Iceburrow. This world has two exits. Completing the fortress will unlock a shortcut to World 6-3: Fog Cemetery. However, completing World D-A will unlock a shortcut to World 6-6: Cawcaw Treeway.


Crystal Caves is a violet cave that has many underground enemies.


Level number Level name Preview Description
D-1 Swooper Cellar Swooper cellar This level takes place in a cave with lots of Swoopers.
D-2 Toxic Wigglershift Toxic wigglershift
D-A Carapace Catacomb Carapace catacomb This takes place in a catacomb, as the name implies. This has Halloween as the goal pole area.
D-3 Spine Springs Spine springs
D-Fortress Toxic Fortress Maxresdefault (1) This level takes place in an underground fortress filled with poisoned water. Some of the floors/walls drop upon touch, so be careful. There is no boss in this level as with all of the lettered world fortresses.
D-switch Red Switch Palace Red switch palace The Red Switch Palace can be accessed via the secret exit in 5-5. If the Palace is reached before Crystal Caves proper is unlocked, its world name on the map will read "???".

Other Buildings


  • The music of the levels is a remake of the underground theme from Yoshi's Island.