The Forcebar
This short, well-traveled passage is named for its intended defensive use. In the event that Waterdeep is invaded, huge sections of stone wall can be magically brought from the ethereal plane to block major roads in the city at strategic points, forming an inner ring of defensible walls. Just south of this alleyway one such wall will block the High Road - and the Forcebar, along with Tilman's Lane, will form a route for defenders along the inside of this wall.
Although at least one gang has used the Forcebar to crash caravan wagons on the High Road by spurring fast carts out of it into contact with them and then launching a sudden and well-armed attack on the goods and wagon crew this passage is heavily used by both the city guard and the city watch, and so is fairly safe.