8 cubes in a loop, making a fidget that moves in a number of ways including turning. This one turns very satisfyingly, not only one handed but no-handed; if you put it in your palm and jiggle it up and down it will turn itself. (Printing it in stripy filament will make this effect more obvious.)

Usually prints well with only critical supports.

For the loosest, simplest version, try the basic cube loop. For a version that is slightly looser, making for a cleaner turn, but still has space in the middle try the one with bars.  The most impressive is cube in cube which is also a bit larger. If you want something that's difficult to turn, try the one with plates.