World 1-2 (Super Mario Bros.: The Lost Levels)

World 1-2 is the second level of World 1 in Super Mario Bros.: The Lost Levels and the second level overall in said game, taking place underground.

Layout
When the player starts the level, their character will begin walking into a Warp Pipe, taking them underground.

The player falls onto a stretch of land with a Koopa Paratroopa jumping towards them. Across a water pit (an empty pit in the Super Mario All-Stars version) are some stone stairs, above the end of which is a Brick Block with a power-up; if the power-up is a Super Mushroom, it will begin sliding to the right and the player can collect it after passing a pipe with a Piranha Plant and some Goombas, but if the power-up is a Fire Flower, they will not be able to collect it as the block is too high to jump onto. Within one of the Brick Blocks past the first pipe is a Coin Block. In the left-most Brick Block above after a second pipe is a beanstalk that leads to an area with Coins and a Warp Zone leading to World 3-1. To reach the beanstalk, the player can find a Hidden Block between the blocks and the pipe.

Past the beanstalk is a set of stairs, above which are Brick Blocks containing either Super Mushrooms/Fire Flowers or 1-Up Mushrooms, which will move above a chasm with four lifts that will fall when the player steps onto them. If the power-ups are Fire Flowers, the player will have to break the middle blocks to the left in order to use the other set further to the left as a platform. After the falling platforms are several pipes with Piranha Plants. Underneath the floating pipe are some Brick Blocks, with the left-most block containing a Super Star. The blocks are placed over a chasm, so the player has to jump at the block at an angle or from the ledge in order to avoid falling in. After the pipes are a trio of Koopa Troopas that move under some Brick Blocks, one of which in the middle is a Coin Block. Next is a falling lift followed by some vertically moving lifts before the Warp Pipe to the Goal Pole, which has two Hidden Blocks before it.

Using the lifts before the final Warp Pipe, the player can jump over the pipe to reach a Warp Zone to World 2-1. The first Warp Pipe in that secret area will also lead to a different area. This area first has a row of ? Blocks, with the right-most one containing a power-up, followed by falling lifts and pipes with Piranha Plants over water pits (lava pits in the Super Mario All-Stars version). In order to cross the pit of water after the third pipe in a powered-up form, the player needs to crouch and slide to break the lower two brick blocks, then they will be able to run across the pit. If they are not powered-up, they can simply run across. The next pipe will take the player to a Coin room with a Bill Blaster, which will lead back to a pipe before the exit of the level. However, finding two Hidden Blocks after the pipe leading to the Coin room will allow the player to reach a Warp Zone leading to World 4-1.