looking for a few ideas.

I'm looking for some fun projects to help myself learn to build complex things.
I was thinking something like a combo-lock using buttons, but i am not sure.
Hoping JSP could throw out a few things i can try making with redstone.

Please explain, the purpose, the function, and other things needed to know, I will design and build it.

A stairway that folds up to a wall so you cannot tell it's there. Combo safe locks, whole room electric lighting using glowstone &sticky pistons to block them off. A really complex one is a full song/rhythm using note blocks.