OK, here's one, which is something I need for a possible story...
What if you were trapped in what you think is a 3-D box, and it suddenly starts to go 4-D with you inside, rotating in the 4-D axes, then restores itself bact to "normal" 3-D, from which you can finally get out of the box?
Or, if you want it put this way, what would it be like inside a 4-D box- What would it look like?
d.m.f.