World 7-Ghost House (New Super Mario Bros.)
From the Super Mario Wiki
In this level the player must hit the first of a row of Brick Blocks to release a ? Switch that will make five doors appear when hit. The middle-left door and top doors leads to the rooms containing a Star Coin for each. Neither the middle right door nor bottom left door are necessary to finish the level or get all three Star Coins. The bottom right door leads to the exit. Inside is a group of Phantom Hands who direct the player to the moving box that contains a ? Switch. When hit, two moving platforms appear for a short time that bring the player up to the next door. In this new room, the player can hit a P Switch that for a short time turn the surrounding coins into solid platforms. Here, the player can take a shortcut to exit the level by climbing a hidden vine to the left or take the standard route out to the right. The third Star Coin is in a high platform at the top right corner of the room, and the player must be quick to reach it. Once the player leaves the exit door they are at the black flagpole that ends the level.
When the player is in the area with the P Switch, they must press it and then go to the left. One of the blocks on the upper ledge shines, different to the others. If the player hits this block, they will find out that it contains a Beanstalk, and climbing on it will take them to a door. The door leads to the secret exit's flagpole, which unlocks access to the 1-Up Toad House between level 7-3 and the tower.