Just a sort of ball maze I put together from a handful of basic elements. It's one continuous loop for a 12mm steel ball. Printing it with FDM could b...e a bit tricky I'd guess.
Should be possible to print with SLS and then click the ball in.
Added a version with a 12mm ball for SLS printing.
This is an extended version of a thing I made before and printed with grey PLA on an FDM printer.
Since I don't have a dual extruder printer, I ordered a white thing in ABS from Reputech ( https://www.3dhubs.com/service/reputech
). He did an excellent job with solvable support material.