Climb on the ledge beneath the low chandelier (which is close to the entrance) and from the highest point, jump up to grab the chandelier; pull up.

Turn around and take a running jump to grab the middle chandelier; pull up. Turn right and take a running jump to the wooden platform. Use the switch to reveal an opening behind the painting at the other side of the room.

Take a running jump back to the middle chandelier and turn right. Take another running jump to grab the third (higher) chandelier and pull up. Climb on the wooden platform and kill the two rats that are coming from the right.

Go to the right behind the column (where the rats came from)...

... and grab the wooden rafter above. Shimmy to the right and pull up.

Take a running jump to the wooden platform ahead and draw your weapons. As soon as you the reach the brick wall, a thug appears from behind. Kill him and pick up his Small Medi Pack. Climb on the brick wall and turn right. Jump to the other part of the rafter and use the switch to change the height of the first and third chandeliers.