This figure shows a 3 by 3 by 3 unstructured grid in the shape of a cube. Each of the 27 nodes is numbered.
Nodes 1-9 are on the back face of the cube, with nodes 1-3 on the bottom, 4-6 in the middle, and 7-9 on the top. Nodes 10-18 are on the mid-plane of the cube, between the back and front faces, with nodes 10-12 on the bottom, 13-15 in the middle, and 16-18 on the top. Nodes 19-27 are on the front face of the cube, with nodes 19-21 on the bottom, 22-24 in the middle, and 25-27 on the top. All nodes are numbered from left to right as seen from the front of the cube.