an egg.
location: run up to the elevator and press down. you will climb down the edge. jump to the chain here and climb all the way to the bottom to find an egg.
location: jump to the panel to reverse gravity and a crate will join you on the ceiling. use it to jump back out to the entrance. run outside and you will fall up to a secret spot on the roof. run to the left wall and pull the handle here to reveal an egg. stomp on it for the achievement/trophy - going up. 