"In 2013, a friend took me down the railway tracks behind Klong Prem prison. I saw this forest of cement columns covered in artwork and I was instantly attracted," says photographer Rupert Mann, author of "Bangkok Street Art and Graffiti."
"There's no other place like that I know of in the world. It was like walking through a politically charged art gallery. And there were artists working there. I thought, there's a book in this, and that's how many interviews began."