Climbing Wall

The Climbing Wall is a giant wall which campers climb at Camp Half-Blood. They must climb quickly or it will clash with the other wall, causing lava to pour from the top, and boulders to fall on whoever is climbing.

The Lightning Thief
The climbing wall is mentioned when Percy Jackson talks about his days after having found out he is a child of Poseidon. He says that Grover Underwood could quickly climb up to the top and that Percy barely made it up. His Camp Half-Blood t-shirt had smoking holes in it and the hairs on his forearms were singed off. He later says that he could climb to the top on the best level without getting burned.

The Sea of Monsters
The climbing wall is mentioned in Percy's report card at the back of the book. It features a grade for the climbing wall in which Percy had received an A and the comment from Chiron reads: "Percy excels at rock climbing. Perhaps it's because he does not enjoy falling in the lava below."

The Titan's Curse
When Nico di Angelo first arrives at Camp Half-Blood, he notices the climbing wall as he is climbing off Apollo's sun chariot (in bus mode) and asked Percy about it. It is then that he asked why there is lava pouring down from the top, to which Percy replied that it's just for a little extra challenge.