A Triangular Box is a 4dancer formation in the following shape: EN: 20 
From Interlocked Blocks, there are two Triangular Boxes:
to find them, divide the formation in half along the phantom long diagonal.
Alternatively, look for a Diagonal of 3, then find the lonesome dancer. EN: 30  
Other examples of Triangular Boxes: EN: 40 
Triangular Box Counter Rotate 1/4 :
