A Hidden Treasure is a side quest in Egypt (Act II). It is given by Asri, a scamp standing in the north-western area of Fayum Oasis. He tells you of an ancient tomb, where lots of treasures can be found.
The tomb is located to the far north in the region, beyond the Dune Raiders camp. It's a fairly small tomb and the treasure chamber can be found behind the large door. Be careful though, as there are usually lots of undead and Dark Obelisks guarding it. Entering the treasure chamber completes the quest. In the treasure chamber you'll find a Majestic Chest, a Royal Chest and some smaller treasures.
You can talk to Asri after completing this quest to hear him getting mad about it, but nothing else will happen.
Reward: 9000 experience