This is based on the plot Z=X*Y (known as a hyperbolic paraboloid or a saddle point) but instead of being a continuous surface, I've discretized it so that it is formed from a collection of varying height square prisms.
Aside from looking great, it feels really nice to run your fingers over the discretized surface.
4.83 w x
4.83 d x
1.902 w x
1.902 d x