One of the most recognizable woodcuts by German master engraver Albrect Dürer, dated 1514.

A nice large scan of this piece can be found at:
http://web.ionsys.com/~treb/images/durer.html

The title of the piece, particularly the "I" suggests that Dürer may have originally intended to do a series of four pieces, one for each of the Four Tempraments (melancolic, phlegmatic, choleric and sanguine). This is further supported by the existence of a fourth order magic square (i.e. contains the numbers 1 through 4).

Melencolia I contains many allusions to alchemy, as alchemists were often seen as perpetually melancholy, frustrated people. Their constant, perpetually fruitless quest for the Philosopher's Stone tended to leave them to an endless series of defeats.

Some likely refrences to alchemy:

Some scholars suggest that the magic square may contain a reference to Dürer's mother's death on 5/17/1514.