Leo shows his cabin mates that he can use fire, and they are appropriately impressed.
He also shows them the secret Bunker Nine. They are even more impressed than before.
They find Festus's head, which Hephaestus brought here so Leo could reuse it.
There are lots of blueprints for weapons and such, too.
Chiron explains that the bunker was built during the Civil War, when demigods fought one another (conveniently at the same time as the American Civil War).
One side in the war was Camp Half-Blood, and the other side was the Roman camp.
They look at the blueprint of a ship on the wall and realize it's just like Leo's crayon drawing when he was a kid. Also, Festus is the prow of the ship.
Leo says he'll build the ship and call it Argus II. Then they'll fly it to Greece.