Two mirror image pieces assemble into a hollow polyhedron with curved faces. The final shape is the solid defined by the intersection of three cylinders at right angles, sometimes called a Steinmetz solid or tricyclinder. I call it a Pillowhedron, in reference to Stewart Coffin's Pennyhedron Puzzle which inspired it. This puzzle is surprisingly difficult to take apart. This version is printed in three colors.
The color sandstone works nicely for this puzzle. The fit is quite tight off the printer, I had to rub the joining faces together a bit to get it together. Then it goes together with a snap (literally). Definitely not trivial to get it apart, as the colors help to confuse the issue, and the joints are fairly well hidden.
This puzzle is the size of a ping-pong ball (4cm diameter). Play with this puzzle over a carpet because a drop onto a hard floor will chip or break the pieces.