World 2-1 (Super Mario Bros. 3)
From the Super Mario Wiki
This level mostly consists of stacks of Brick Blocks, along with multiple small pipes serving as platforms.
The player will start in front of multiple stacks of Brick Blocks. Pile Driver Micro-Goombas are hidden among the Brick Blocks, so the player must be careful to avoid being hit by them. Afterwards, the player will encounter a Koopa Troopa near a ? Block containing a Starman. Past this are some Firesnakes patrolling the first few small pipes. While the pipes themselves cannot be entered, they do enclose small areas containing coins and 1-Up Mushrooms. The player must be wary of the multiple Goombas and Firesnakes on and around the pipes. Towards the end of the level are two regular-sized pipes, containing Piranha Plants, surrounding a stack of Brick Blocks, and finally the goal is reached.
There are two hidden rooms in the level; the first one requires Raccoon Mario, and can be reached by flying left upwards on the first pipe platforms. Inside is a Switch Block, which will produce Blue Coins in the room, and also provide access to certain blocked-off sections outside of the room. The second hidden room is found in the pipe closest to the goal near the end of the level; inside is another Switch Block, which can be used to turn the stack of Brick Blocks outside into coins.