This page in our guide for Assassin's Creed: Odyssey contains information about the tomb found on Abantis Islands archipelago which consists of Eubea and Skiros islands. Here, you can find a detailed walkthrough for the tomb as well as information on the weapons that can be found there.
Tomb's location: Eubea, the northern part of this island.
Watch out, Artemision Tomb is full of snakes. Start swinging your sword every time you enter a dark room.
Walkthrough: Go inside and reach the end of the path - the passage is blocked by a pillar. Jump above it and move forward.
In the next room, you must jump into water and dive. Swim along the walls to reach the end. Get out from the water. Go up the stairs, move the shelve and you will reach the room with an Ancient Stele and a chest.