World 6-3 (Super Mario Bros. 3)
From the Super Mario Wiki
This is an level made mostly from Ice Blocks. The level starts with two Note Blocks and a lift. After this, there is a ? Block with a Super Leaf and a few rows of Ice Blocks. Then, there are a few Brick Blocks, one of them containing a Beanstalk which leads Mario to a secret area with a Tanooki Suit and Coins. Next, there are a few more rows of Ice Blocks, a hidden 1-Up Mushroom (which appears fully-white in the original), a lift, two Koopa Paratroopas, and the goal.