u can find an informal kind of gallery in hamburg, where free street art artists came together to protest against grey and ugly places in thier city.
i don't know exactly when the illegallerie was made, but today many of the great paste-ups are destroyed. it's kinda sad to see only the rest of the pieces, but that's street art, too - quickly gone!
my favourite work is the one of "mindfuck", at least one of those pieces, which are sill intact...
haubachstraße, hamburg-altona (holstenstraße)
more illegalleries here: