There are three Keycards: red, blue, and yellow. Once you find them all, a door in the Treehouse opens to reveal the Chalice of Power.

-Red: Near a police car on the second set of them. You have to fall to your death to get it. (Clank)(Asyanica)
-Blue: Once you get on the second mine cart, go backwards instead of forwards. You'll find it there. (Gadgebots)(Fort Sprocket)
-Yellow: On the last path to save the Space Nuns, don't use the cannon at the very end. Instead, jump off that gray area towards the Kudzu's eye. Press X again, and you'll get blasted forwards and achieve the yellow keycard. (Qwark)("Saint Qwark")(Spaceship Graveyard)