He was familiar with the area, but there wasn't anything that would make a suitable target for releasing pent up anger. So he was forced to admit that no, he doesn't have any suggestions. (Just what was a gym anyway?)

"Not really. Just try not to hit a tree, okay? They can't move or smile or talk, but they're still alive, ja? ...maybe a dead one instead." But how many dead trees were there? Pondering this, Cielo comes up with a different idea and snaps his fingers. "Or you could hit me, I'm tougher than I look."

He's hit plenty of times! Even by things that could, yes, leave cracks in trees.