Willy's House is a residence on Lanilor Lane in Aleroth during the events of Divinity II: Flames of Vengeance. It is located across the road from Alzbeta's Emporium, between Madame Eve's & Sir Gula's House. It belongs to a con man named Willy, and the door is locked unless you agree to help Willy for the quest A Swindler Swindled when he is initially encountered west of the Great Market waypoint shine (see Aleroth Maps).
On the west side of the house there is a locked wooden chest. The key, along with a Bellegar Coin (required for the quest Mind over Matter), can be acquired by looting the citizen's corpse that is found on the elevated platform directly in front of the chest.
On the east side of the house, you'll find a trapdoor to the Playhouse Cellar (locked), a golden chest (locked), and a golden key under a pile of zombie corpses. Gaius and Vito are there as well, arguing about to what to do with the corpses. If you side with Gaius, then leave and return (e.g. enter any building then come back), he will have burned the corpses allowing you to pick up the golden key and use it to loot the nearby chest (containing random loot). If you side with Vito you'll gain 6000 exp, but are unable to loot the key.
An alarm switch (#2 on map below) on the desk can be pressed, either by Willy (if you side with him) or by you (if you choose to press it after siding with Brancussi). The alarm activates several fire traps throughout the house, injuring everyone within and opening the locked door (#4) to a room which contains: a lever to disable the alarm (#5), a book titled How to Pull a Willy (and get away with it) (#7), and a chest containing random loot (#6) that requires lockpicking level 3 or higher to open. Inside the main area of the house you'll also find an unlocked chest containing more random loot (#3).
If Willy is the one to press the alarm a battle ensues with the Assassins' Guild members, leading to Brancussi's death (he drops the Shadow Archer Cuirass when killed). If you sided with Brancussi, you can purchase the Shadow Archer Cuirass and other items from him. Be aware that pushing the alarm yourself causes the assassins to flee, preventing you from trading with Brancussi any longer, so be sure you've bought everything you need from him first.