Sly must go through an alley up ladders, on fire escapes, on gargoyles, and jumping on air conditioners to get to one of Muggshot's Treasure Keys. Once he succeeds, he's ready to face the enforcer of the Fiendish Five, Muggshot.
The bonus commentary for this level says that this was an introduction to bouncing objects, like trampolines or awnings. They also found the air conditioners interesting, since they fall after you jump on them, and it's like a test of the player's skill.
They also played with Sly's lesser known abilities, like ducking behind rocks, precision and parkour.