Newer Super Mario Bros. Wii
|Game(s)||Newer Super Mario Bros. Wii|
|Previous world||(5) Freezeflame Glacier/Volcano (sec.)|
|Next world||(6) Pumpkin Boneyard|
Crystal Caves (or World D) is the fourth secret world of Newer Super Mario Bros. Wii. It is unlocked by completing the secret exit of Magma Iceburrow from Freezeflame Volcano, but can also be partially unlocked by completing Snowfall Peak's secret exit. This world has two exits. Completing Toxic Fortress will unlock a shortcut to Fog Cemetery, however, completing Carapace Catacomb will unlock a shortcut to Cawcaw Treeway. Both of these levels are housed in Pumpkin Boneyard.
Crystal Caves is a violet cave that has many underground enemies.
|Level number||Level name||Preview||Description|
|D-1||Swooper Cellar||This level takes place in a cave with lots of Swoops.|
|D-A||Carapace Catacomb||This takes place in a catacomb, as the name implies. This has Halloween as the goal pole area.|
|D-||Toxic Fortress||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-||The 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 "???".|
- Challenge House H can be accessed after completing D-1.
- The Crystal Music House can be accessed after completing D-A.
- The music of the levels is a remake of the underground theme from Yoshi's Island.