Sunset House - Extra things to get
You'll find the Demon Door to the left. It should be easily spotted since there's some braziers lighting it up. You need to be the Queen or King of Albion to meet its condition. Look to the left past the ruined arch and pillar to find a Silver Key as well.
From the manor's entrance, head to the right until you find a dirt path. Follow this and you'll find a golden door. Go uphill; there's a Silver Key behind the tree a bit north of the golden door. Further north of the Silver Key you'll find a pond. The area's only gnome is on the rocks.
At night the destroyed house is fixed again. Head to the pavilion and discover that gazebo is glowing blue. You can now interact with the statues there. You need to press A on each statue until they resemble their solid poses during the day. To make it easier, you need to change their poses 4 times. If done correctly the phantom house will materialize so you can enter it.
Warning: You won't be able to leave this house until you complete the quest.
Enter the house. You'll find a hanging skeleton there. Examine the note beside it to learn more about the curse. Ignore the warning and follow the trail. Sleep on the bed and you'll be taken in another dimension with a large chessboard on it. Talk to the chest in the middle of the board named Chesty. Start a game of chest with him.
Just play chess as you normally would. After a few turns he'll get bored and will have the chest pieces attack you instead. Speak to Chesty after defeating each wave. After getting rid of the last pieces, talk to him again to complete the quest. Your reward is 20 Guild Seals and the house itself. You'll be taken back to reality afterward.
Don't leave yet; there's still some stuff to do here. Take the new corridor as it leads you to another room with a mirror. If you look at the mirror, you won't see your whole reflection. Instead, you'll find a floating head which is your head. Look closely at the mirror and change your camera angle to find a glowing seal on the wall. You need to guide the glowing head on that seal. Watch the video below for more information.
Sunset House Mirror vault
Doing this three times will allow you to vault over through the mirror to the house's alternate side. Head to the entrance and shoot the green ball on the table to unlock the other door.
This will lead to a chest with a legendary weapon (I found a Thunderblade sword). You can also check the master bedroom to find a chest with health potion. Check out the shelves for some random goodies as well. Return to reality then shoot the green orb behind the hanged skeleton. This will also open the locked door, leading to a chest with possibly random loot. (I got 6 Guild Seals and a Slow Time Potion from this chest)