Once you enter the level, climb up the ladder and find two clues on the fire escape to the left. Climb up to the rooftop and take out Inkspot Jackson and collect more clues. Then climb onto the next rooftop to run into Carmelita. Hop onto the next rooftop to find more clues and a Lucky Charm. Bounce off of the mattress to get onto the flag pole and hop on the small water tower to get to another one. Collect more clues and then bounce off another mattress to jump onto the casino sign. Spire jump across the sign and continue across a few more rooftops to reach the top of an apartment building. Collect the clues, then bounce off another mattress to reach a clothesline. Shimmy across the clothesline to the scaffolding, then run across the boards to reach the raised section of the roof. Grab the clues at the opposite end of this roof, then jump onto the next clothesline, which will fall and send you flying into the next building. Continue climbing up the line, and once on top, grab the single clue, then jump down into the old casino.
Once inside this place, you will lose Carmelita for a little bit. There are more clues to collect and three more guards to take out. In the next room is the vault. Collect the remaining clues to unlock it. After that, continue on by hopping across the chandeliers, game tables, and small, hanging metal bridges. Continue jumping as Carmelita will shoot each object down. Once you reach the end, break the fire hydrant. The fire hydrant has a rope connecting to the Muggshot float Carmelita is standing on. Break it to send her flying away and then grab the key.