the galeria arte urbana (GAU) is an outdoor street art gallery located on calcada da gloria, next to the upper station of the elevador da gloria. the six large walls are painted by different artists and get repainted every once in a while.
“The GAU – Urban Art Gallery – is now closer to everyone.
We went from 7 panels installed on Calçada da Glória | Largo da Oliveirinha, to walls and facades, to waste collection trucks and bottle banks that can be discovered throughout the entire city….” source
a bit further down the road even more street art can be found:
more street art in lisbon can be found in this post or at the LXFactory.
more about the galleria arte urbana: gau-lisboa.blogspot.com and galeriaurbana.com.pt (both only in portuguese)
Big Cities. Bright Lights. 
So cool! I love the knitted tree in the second to last photo.
Love the yarn=bombed tree.
Good lord, I adore street art (no big surprise there). This is some really great stuff. I especially like that tree whose bark has covered with a colorful design (how did they do that by the way?). Gorgeous!
Seems like everybody loves the tree! I did, too!
BTW: http://www.lisboaimages.com has awesome shots of street art/murals/graffiti in Lisbon, in case anyone is looking for more.