Another Elevator is an Watch floor where you will be teleported into a different elevator. After about 5 seconds the lights will turn off and then you can hear squeaks. After 2 creaks the floor explodes, you will start falling down onto another elevator. After all this, relaxing music starts playing while the elevator is moving upwards. You will eventually be teleported back to the original elevator.
Fun Fact: You can stand on the very edge of the 1st elevator and can stay on it after the floor explodes.