You will not be able to enter the attic until you are near the end of the game. After you have collected all of your notation notes from the resort's various rooms, you will be challenged to play several tunes on the organ. After you have successfully played the correct tunes, you will receive tokens from the organ monkey. Insert these tokens into Isadora's coin slot. After you have inserted all of the tokens and heard her revelations, she will offer you a key. This is the key to the attic. Take it to the First floor hallway and insert the key. The attic door will open. Your mission in the attic is to get the piece of the elevator control panel and return it. Then head down to the Basement. In order to do this you must first make it across the chess board with the toys on it.
In order to get across the floor you need to pay attention to the patterns that the toys move in, or you'll be bounced back. An easy way to get past the toys is to move straight ahead as quickly as you can. Once on the other side, you can reach the Toy Box, the Teddy Bear and the Elevator. When you reach the Teddy Bear, he will tell you to look in the Toy Box for the piece of the Elevator that allows you to get down to the Basement. This piece looks like an ammo box. Place it in the appropriate slot on the right hand side of the Elevator and you will be able to travel to the Basement.