A hyperbolic tessellation in Poincaré’s disk model, using only regular heptagons (light blue). Connecting the midpoints of adjacent heptagons gives a tessellation with hyperbolic equilateral triangles (dark blue), in groups of seven around common vertices.
This kind of hyperbolic patterns, published by mathematician Harold Coxeter, inspired Maurits Escher to his famous Circle Limit woodcuts.

A hyperbolic tessellation in Poincaré’s disk model, using only regular heptagons (light blue). Connecting the midpoints of adjacent heptagons gives a tessellation with hyperbolic equilateral triangles (dark blue), in groups of seven around common vertices.

This kind of hyperbolic patterns, published by mathematician Harold Coxeter, inspired Maurits Escher to his famous Circle Limit woodcuts.