How about traveling to the past and discovering how things really happened. If you decide to do this you will just have to sit back and observe, letting things unfold as they did because even your thoughts could color the events within the dream. In other words, you are going to have to become the ultimate dispassionatly objective observer.
Brent
why not create a lucid house?
like, go into a white space an empty space and create a house and an enviorment around it. then revisit it in your dreams.
sorry if this has been said before
Hey, we could combine yours with mine! Gon inside LD4all, find a topic you like and build a house/ base there!
yea 
Gravity based tasks:
Turn gravity off, make it stronger or weaker, make it go in a different direction, change only how it affects you so you can walk up walls, or change only how it affects DCs so they all fly into space.
Mirror based tasks:
Enter a mirror, pull your reflection out of a mirror, switch places with your reflection and see what it does, turn the mirror into a portal, fight your reflection, get your reflection to give you stuff, change your appearance, or grant wishes.
Hola!,
Make a future - Turn into someone else and create their future. Or – Make your own future.
-Alex K
If you play computer or video games, enter the game and beat it or just have fun playing in the game world 
Create a box; reach your hand in and see what you pull out.
Ask a DC what he/she/it want to do and then during the LD help him/her/it fulfil the wishes.
Could be interesting to follow another DCs wishes instead of your own 
Create a time paradox. Stop yourself from being born, or kill a past self. Kill an Homo Erectus so there willl be no Homo Sapiens, etc.
Travel inside your own body.
Grow eyes behind your head.