A delightful surface: the gyroid put through a simple inverse transformation. It's ellipsoidal on the outside, and there is a sphere taken out of the center, which is difficult to see; for otherwise it would be infinitely tiny inside, and therefore unprintable.
The Schwartz D ("Diamond") surface is a triply periodic minimal surface, like the Gyroid. Here it's been translated in both normal directions, and one of the two resulting (identical!) surfaces networked. Another Schwarz surface is in metal here: http://bathsheba.com/math/schwarzd.