Outlaw art (most of the times) in the urban landscape, in other words, Graffiti.
Travelers to Athens can't help but notice the amount of graffiti in the city. Any surface that can be sprayed upon is covered with a maddening number of scribbles, slogans, signatures, and designs, but there is also a large amount of graffiti that is good art.
Walking around Athens especially at Plaka, Gazi, Psiri, Metaxourgio and Exarchia districts you may discover amazing pieces of art in the most unexpected places.
ILPAP Building houses the city trolley buses and it is located at the end of Ermou Street where it meets Pireos Street in front of the Gazi, the city's former gas works and now a center of arts and entertainment.
At its wall, there is a huge graffiti that was painted by a group of well-known international graffiti artists.
The building it is not been kept up and could use some restoration but is impressive for its size, design, and colors.
If you are interested in street art you may want to follow the “Athens street art tour”. Your guide will be a street artist who will show you the details of the coolest works of art in the most unlikely places.
http://www.alternativeathens.com/tours/street-art-tour/