On this page of our guide to Uncharted 2: Among Thieves you will find a detailed description of secrets and collectibles available in Chapter 2 - Breaking and Entering. Our step-by-step walkthrough explains how to find all (10) secrets hidden in the second chapter of the main campaign.
You'll find the first secret right after you leave the sewers, in the boiler room. Its in the corner of the room, on a crate.
The second item is on a small yellow platform, towards which you will have to jump in order to grab a ladder. You will find it just after climbing to the upper part of the boiler room, next to a place with a cracked pipe that emits a lot of steam (before, not after).
The third secret has been hidden among the exhibits in a room with doors secured by an alarm. You will note it during a cutscene (the item is located next to the sculpture).
After you separate from Flynn (he will ask you to go left while he goes right), and after killing the first enemy, jump down and turn left towards the next one. There, on one of the flower pots you will find a hidden item.
The fifth treasure is most visible. It is located in the fountain, in the central part of the open space where you can get by opening the gate secured with an alarm.
The next item is located in the upper part of the room where you will get a dart gun. The treasure lies near the window, which can be reached by passing through the rafters (you will walk on them in order to get to the roof).
Treasure no. seven is the most tricky one as it's well-hidden. In the spot where Flynn takes out the rope for the second time, you'll be forced to grab it and swing on it (this is the first time that this mechanism is used in the game). The further road will lead up the wall of the building, over the grating, but you have to go down and jump on a white ledge. Walk on the ledge and get around the corner of the building (as shown by the arrow), and then approach the second sewage pipe sticking out below you. Jump on it and lower yourself on its edge. This way you'll collect another treasure.
After the other guard has been put to sleep (do it while hanging), jump to the place where his body is located. Go straight ahead and jump down on green roofs. There, walking a few meters ahead, look behind the corner of the just passed building. At the top, next to the red flag, there is a hidden treasure. Shoot at it and collect the item.
The last two are at the end of the stage, while you are escaping from the guardians. The first one was hidden in the room where the chase will start. It is located in the recess of the wall next to the grating, behind which there will be three guardians.
The other one is in the sewers, in a room with many pipes. You will find it opposite of the entrance to the next room (it's the last treasure that can be found in this chapter).