Per the Wikipedia article,
The Lennon Wall is a wall in Prague, Czech Republic. Once a normal wall, since the 1980s it has been filled with John Lennon-inspired graffiti and pieces of lyrics from Beatles songs.
During my meanderings around Prague yesterday afternoon, I finally found it, though by accident. Most of the original Lennon art is gone and covered up by other things with a fair amount of Beatles related graffiti.
