How many ways are there to breach a castle?

The direct approach--break down the door with a battering ram, throw grappling hooks over the walls and climb, break down the walls with catapults, sneak inside a big wooden horse, dress up as someone who works at the castle, offer terms of surrender and attack once they let you inside, go stealth and climb through the sewage system, dig a tunnel underneath the wall, fly over with Leonardo DaVinci's flying contraption, and that's about all I can think of. What's the most creative way to break into a Castle, any famous incidents that made history?