On this page of our treasure guide to Uncharted 3 Drake's Deception you can find valuable information about all collectibles available in chapter 21. While exploring Atlantis you may come across five different treasures. Don't rush to the next areas of the lost city, because you might lose time required to collect some treasures.
Bronze Man of Nashqum
Immediately after entering the lost city, descend the first staircase and go to the crossroads. Take the stairs on the left  and move down to find a treasure on their edge .
Sabaean Alabaster Stele
Immediately after entering the lost city, descend the first staircase and go to the crossroads. Go down the stairs on the right. Stop by the tower on the left and jump in through the open window . You can find a treasure lying in the middle of the room.
Akkadian Statue Head
Immediately after Sullivan's death go right  to a richly decorated building. At its end, you will find a treasure lying above the stairs .
Sabaean Moon Symbol
After escaping from the spiders, you will wake up in the elevator as an intoxicated adult Drake. Turn back and head towards the monument standing by the wall . You can find a treasure on your way.
Statue of Gudea
After solving the pool puzzle, during which you can see Drake's reflection, you will end up in a room with human remains. Leave this room and enter a corridor , where you can find a treasure  hidden behind the second statue on the left.