Want some fun experiments to try for Lucid Controlling, or initial entry? Come up with sufficiently exotic locations. Like an environment that is constantly falling, but has no freefall antigravity. If you're overly realistic in order to create it, you can always justify it as orbiting something really quickly, to the point of feeling like falling, and is super-dense enough to keep some level of relative gravity intact. With those justifiers in place, it should be BS-ed enough to be observable.
Just come up with some thought experiments like that (justifying the impossible is also fun to do at times), and come up with some clever ways of lying to yourself to get away with it. Pull a fast one on yourself, and have some real fun. Other ideas also include having a mini-planetoid kind of central hub that can be rearranged like a Rubik's Cube. Hell, have a negative-space variant of it as well, where the faces are instead walls,
and you're inside the said cube. Add more variety, each face of the cube is a doorway or a piece of the overall environment (when solved, could look like a study, or your own bedroom). Speaking of which, why not step it up, and make that place an entire house, each face is another room of the house; and everything's as easy to rearrange as rotating a row or column, or walking up/down a corner.
EDIT:
Another interesting idea is being on a planetoid moon (like a small temple or shrine on the mini-moon of a moon) that's orbiting a moon that's orbiting a larger planet; and just watch the days and sub-years pass by per sub-orbit-cycle. There have been moons found with moons of their own, right? Is that possible to render?