Take a look at the John Lennon-inspired political graffiti which constantly changes. When Lennon was killed in 1980, this place became a sort of fictitious memorial, commemorating the singer. People soon started to cover the wall with Beatles songs' lyrics and various quotes celebrating love.
The wall has recently been painted pure white, with the words „Wall is over“ written on it. It was painted by a street art group as a celebration of the 25th anniversary of Berlin Wall's fall. Later it has been changed to "War is over" and now it is again covered with a snarl of colors.
The current decision by the owners of the wall states that it's going to be used only by artists who will be approved beforehand. Therefore, to paint freely on the wall will no longer be possible as it has been used for touristic purposes and lost its original meaning along the way.
Wikipedia https://en.wikipedia.org/wiki/Lennon_Wall
Address Velkopřevorské náměstí 490/1, 118 00 Prague 5-Malá Strana, Czech Republic
Coordinates 50°5'10.412" N 14°24'24.659" E