This level has a windup key in the back that makes the right and left sides. There is a Spike throwing spike bars down the center. Go to the right side and you'll find the first gem in the hallway under the second tier. Walk around to get it. Go to the center to reach the second tier on the right side. Go to the third tier and cross to the center when the hallways line up. In the back is the third gem. Go to the left side to find the second gem. Reach the area on the same level as the Spike. Cross to the other side of the Spike and you'll find a hidden Gold Mushroom near the Star. Use the right side of the area to reach the area above the Star. Drop down on the Spike to defeat it and the wall to the Star will open up.
Special Challenge: Find the hidden Gold Mushroom.