To be able to reach the door in the attic that allows you to enter World 1 you must first repair the ladder in the house (level select area). This is done by finding ALL 72 puzzle pieces and assembling each world's jigsaw puzzle. When you have beaten World 1 you will be taken directly to the Epilogue which you can return after beating it any time you want by walking into an offscreen alcove which is reached by going left at the 'Title' screen.
When you have collected ALL 7 of the secret stars an 8th star will be available in the final level and some of the switches will become immune to time manipulation allowing you to reach the 8th star and change the ending of the game.
When you reach the second-to-last room just before the castle in the Epilogue jump from the elevated platform onto the middle of the bridge (rock) and if you perform the move correctly you will hear a confirmation sound and a new journal entry will appear.