This is what happens when you peel off a piece of wall that is layered with 30 years of graffiti.

Doornroosje is a concert venue and graffiti hall of fame in Nijmegen, the Netherlands that began as a 70's hippie hangout and one of the first places where it was legal to smoke cannabis. The building is surrounded by walls that are spray painted from top to bottom. Imgur user Paul DeGraaf removed a section from the wall (circled area) and photographed the layers of paint that had built up over three decades. They resemble the annual growth rings on trees.

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