This section of Assassin's Creed: Odyssey walkthrough includes the information of tombs located in Naxos. Below, you can find the exact location of the boards at the end of each tomb and the list of weapons you can acquire.
Giant Heros Burial Ground
Tomb location: Northern part of Naxos.
Walkthrough: Enter the tomb and smash the wall that seems to be blocked. After smashing the wall you will get to a chamber with a water basin. Underwater, you will find Conqueror's Waistband and a lot of money.
If you do not dive, however, you can complete this tomb very fast. Move the wooden shelf and enter another room. Inside, you will find the board and the chest.