- John Polking's Geometry of the Sphere
- Interactive spherical geometry page
- Fun facts about spherical geometry
- Pictures and a "decision tree"
- Frieze and Wallpaper patterns
- Notations for wallpaper patterns
- Patterns at the Alhambra
- World of Escher
- M. C. Escher dot-com!
- Escher and Mathematics
- Hyperbolic tessellations
- Artist or Mathematician?