A 3D-Pyramid features a wide square-shaped base layer of dominoes, which progressively gets smaller towards the top. The pyramid can be toppled by removing just a single domino from the base on any side.

Building a 3D-Pyramid involves repeating two different types of layers as shown below. If you are unsure where to place the dominoes for the next layer, look down for the largest vertical gaps without dominoes. These should be bridged next.

If the base layer of the 3D-Pyramid consists of n times n dominoes, the entire pyramid will require $$\frac{2}{3}n^3 + \frac{1}{2}n^2 - \frac{1}{6}n$$ dominoes.