The waterlock is a large building on the Wrenhaven River which permits entry to the Dunwall Tower grounds from the river.
In Dishonored 2
The lock has been closed to keep sea-faring vessels from approaching the Tower. Only the exterior is reachable. The side facing Dunwall Tower is guarded by two witches and some gravehounds. The side facing the river can be reached by following some large pipes around the exterior of the building. Two more witches are found there as well as a crate containing a bonecharm and two boxes of Pistol Bullets.
Mission[]
In Dishonored
The waterlock is the point of access for Dunwall Tower. The game opens with Corvo arriving at the Tower via the waterlock. Later, he must return to the Tower to deal with the Lord Regent and is once again dropped off at the waterlock, this time by Samuel the Boatman.