What draws Roy to the rockpile?

To the neighborhood boys, the rockpile symbolizes adventure and mystery, and they are innately drawn to it. In an otherwise fairly urban setting, this formation of rock juts out of the ground, and Aunt Florence once told them that "without it the subway cars underground would fly apart, killing all the people."
On the day he is injured, Roy is looking for an escape, and the rockpile provides just this relief for bored young boys. He and John sit on their fire escape watching "the forbidden street below." As they watch people passing them by, they are envious of the loiterers's ability to go elsewhere and disappear from sight.
Roy is drawn to the rockpile because he knows his friends are there. And sure enough, within minutes of leaving John, he has found adventure with his friends at the rockpile via a huge fight. Roy is injured and has to be carried home.
The boys are drawn to the natural wonder of this rock formation in the midst of their street. They are drawn to the sense of adventure. And they are drawn by bonds of friendship that form at the rock.