The Boston Public Library:

Boston Public Library’s collection shows the broad range of Escher’s talent as a printmaker. Escher worked in a number of printmaking techniques, including lithography, drypoint, and mezzotint. However his preferred print techniques were woodcut, wood engraving, and linoleum cut.

Escher is my favorite artist. The level of detail of these scans is remarkable. Thanks to Jason Kottke for the link.