I'm not sure how he does it, but a Portuguese artist named Alexandre Farto carves murals into walls by setting off small explosions. The above music video for the band Orelha Negra shows the process.
That was lame. It didn't even show the mural before it ended. The little bit it did show of the mural was cool, but not getting to really see it was hard because after about a second, it did a rewind effect.
HAHAHA HIS NAME IS FARTO