This is an extrapolation of the now infamous Penrose Triangle illusion 3D model (http://www.thingiverse.com/thing:6513). If you had trouble getting your head around that one, you're not going to find this one any easier! :)
Where the triangle used 9 cubes, this arrangement uses 31 cubes to make a larger sorta-notreally-cube.
All versions are parallax-corrected for a viewing distance of 40cm.
(the larger ones are not simply scaled up versions of the smaller ones)
pcube10.stl is the 10cm version, measuring 98.32 x 98.41 x 15.14 mm.
pcube15.stl is the 15cm version, measuring 148.03 x 148.15 x 22.03 mm.
pcube20.stl is the 20cm version, measuring 197.39 x 196.83 x 28.77 mm.
(NEW) pcube15_braced.stl is the 15cm version with some bracing between the blocks to help them stay upright in the first half of the print.
(NEW) pcube20_braced.stl is the 20cm version with bracing.
The bigger you can print, the better... however as the photos show, even the 10cm version shows the effect very well!
No support required.