The Wealth of Ancient Kings - Act 4 Side Quest

Start Location: Medea's Grove
Quest Location: Tsakonian Ruins
Objective: Obtain Ancient Moon & Sun Key then open the vault in Great Tomb of Dorus

The Wealth of Ancient Kings is a Side Quest which you can pick up from Carme in Medea's Grove, the second town you visit during Act 4. For this quest you'll need to visit 2 different tombs and defeat the named skeletons inside to collect their keys. Once you have both keys you'll need to go to a third tomb where you'll use them to open up doors and complete the quest.

Ancient Moon Key is the first one to get, you'll find it in the Tomb of Tsakonian Queens in northwestern Soronis (map location below). Defeat Queen Alkiste inside and loot the key she drops. Northeast of the Tomb of Tsakonian Queens you'll find the Great Tomb of Aegimius in the Tsakonian Ruins area. A map location of exactly where to find this tomb is shown below as well. Defeat King Aegimius here and loot his key.

Note: In the Great Tomb of Aegimius you'll also find Nysa, the sister that you need to speak with for The Treasure Hunters Side Quest.

Ancient Moon Key: Queen Alkiste in the Tomb of Tsakonian Queens.

Ancient Sun Key: King Aegimius in Great Tomb of Aegimius.

With both keys in hand you'll want to go to the Great Tomb of Dorus in the northeastern most portion of Tsakonian Ruins, shown on my map below. This tomb is found to the south of Temple of the Gray, the area you need to visit for the Medea's Price Story Quest.

Inside of the Great Tomb of Dorus you'll find locked doors which can be opened with the Ancient Moon Key and the Ancient Sun Key. How this part works is you use the Ancient Moon Key on a keyhole next to the door to open it and then hit the lever inside to open another door. Rinse and repeat, use the Ancient Sun Key on a keyhole then hit the second lever to open the final door.

To complete this quest go into the northeastern most room of the tomb where you'll find a Majestic Chest as well as some other Ornate and Quality chests. Stepping into this room will automatically complete the quest and give you your reward.