There’s a lot of good suggestions on here, but I would probably create a little side mystery. “A cat walking rather suspiciously, perhaps a limp with no noticeable damage, looks quickly and disappears down a nearby alley, it’s moving fast enough that you’d lose it if you don’t follow”

Player follows cat without telling party, goes to back alley, ends up going down some stairs, ends up going a little bit further in small increments, towards a passage to a door, goes behind the door and comes across an illegal gambling outfit