Pratchett's House Exterior.
Pratchett's House is a building located on Kaldwin's Bridge, which can be spotted by Corvo Attano once he passes through a warehouse during the mission The Royal Physician. When Corvo first enters the area, Pratchett and a member of the City Watch will be outside, talking about the curfew (which Pratchett is not keen on).
On the house's third floor, there is a rune to collect and a safe for Corvo to unlock, as well as a note that can be used to uncover the safe's combination, which is hidden in a series of paintings throughout the house.
Gallery
Pratchett's House Interior