The division of waters (1925). Woodcut.

One of Escher's earlier works (part of the "Seven days of creation" series). I really like it for its stunning representation of volume, especially considering the technique used. It's a woodcut printed in black ink, so there are no shades, only black and white. It's pretty amazing...

Day and night (1938). Woodcut in black and grey (two blocks).

Reptiles, 1943 (lithograph). M. C. Escher.