Move Mario up the first broken ladder on the "ramps" level, then climb back down. Walk to the left and position Mario so that his back is almost touching the same broken ladder. Then, move him one or two steps to the right and jump. If done correctly, Mario will fall through the bottom and appear in the "rivets" level or re-appear after several seconds on the top ramp next to Donkey Kong. Note: This only works on some versions of the cartridge.
In the "elevators" level, move to the top right part of the screen to where the purse is located. Position Mario directly above the short ladder and quickly move him up and down to pass through the metal floor.