Arfur's Mansion
Arfur's Mansion is a location in Rivington in Act Three, found directly across from the Rivington waypoint. If you go into the workshop, a Perception check (DC 10) will reveal a hatch leading to the basement, the key to which is on a bookshelf upstairs in his bedroom.
Overview
There are two keys of note to be found in Arfur's mansion; the Toymaker's House Key on a bottle shelf in the kitchen, which opens the upstairs bedroom, and the Toymaker's Basement Key inside a row of books on a bookshelf in the bedroom, which opens the hatch in the workshop.
Workshop
A set of doors on the northern side of the house leads to Arfur's workshop, where he works on his toys. Partially concealed by a rug is a hatch, spotted with a 
DC 10 Perception check, which leads to the basement. This can be opened with the Toymaker's Basement Key from the bedroom.
Basement
The main area of the basement is filled with tripwires and rigged fireworks, which can be exposed with Perception checks. At the back of the basement is another workshop, which has a trapped and locked (DC 20) metal chest, containing a letter which begins or progresses the quest Investigate the Suspicious Toys.
Characters
Related quests
Notable loot
Notable items obtained in this location, whether looted, purchased, or obtained as a quest reward:
Toymaker's Basement Key, inside the row of books on the bookshelf in Arfur's bedroom X: 33 Y: -77
Toymaker's House Key, inside the kitchen, on the top left shelf filled with bottles X: 31 Y: -61
Box of Oddfire Fireworks, in the basement