This page in our guide for Assassin's Creed: Odyssey contains information about the tomb found on Southern Sporades. Here, you can find a detailed walkthrough for the tomb as well as information on the weapons that can be found there.
Tomb of Polybotes
Tomb's location: Kos, northern part of the island.
Walkthrough: Go inside and reach the end of the path, where you can find the first room without an exit. Destroy the vases that block the passage and then go through the hole in the wall. Destroy another passage and then move forward.
Turn right. You will come across a few snakes. Kill them and then move forward. There, you will find an Ancient Stele and two chests. Activate the Stele to complete this tomb. The chests contain Assassin's and Hunter Belt - both items are at level 30.