The Sword Fighting Arena is where campers go to duel and practice with different weapons of their choice. It is between the cabins and the Armory. There are straw dummies in Greek armor scattered around the room and training swords.

Percy Jackson and the Olympians

The Lightning Thief

Luke and Percy practice fighting together at the arena.

The Battle of the Labyrinth

When Quintus (Daedalus) becomes the new sword fighting trainer, he decides that the arena is where Mrs. O'Leary will be kept at. The giant scorpions are also kept in the crates there. Later in the book, when Clarisse is talking to Percy about the Labyrinth at the arena, she casually throws a javelin in between one of the dummies' eyes.

Camp Half-Blood
Camp Half-Blood: Amphitheatre | Archery Field | Bunker 9 | Cabins | Camp Borders | Camp Half-Blood Forest | Climbing Wall | Cave of the Oracle | Dining Pavilion | Grove of Dodona | Half-Blood Hill | Rec Room | Sword Fighting Arena | Thalia's Pine Tree | Myrmeke's Lair | Strawberry Fields | The Big House | The Big House Attic | Zephyros Creek |