House of Lamentation

Located in the Devildom, The House of Lamentation is a huge mansion where the seven demon brothers Lucifer, Mammon, Leviathan, Satan, Asmodeus, Beelzebub, and Belphegor live. After the beginning of the Exchange Program, MC also lives with them.

The house's architecture looks to be Gothic Revival, and there are seven headstones in the front yard. There's also at least one tree within the house, for there's one in the MC's room and one seen in the hallway. It's unknown if these are both the same tree.

History
In Nightbringer Lesson 33-6, Mephistopheles mentions that there's a legend that says that the plot of land on which the House of Lamentation sits used to be home to the father of demons, Nightbringer. Now, this plot of land is owned by the Devildom royal family.

The mansion was originally built in the human world on the outskirts of a village. The people who previously lived there were a married couple with their seven children, and their servant.

One day, a terrible tragedy struck inside the house. Every family member was brutally murdered in a different way, in a different room, and the servant had hung himself in his own room. The only survivor was the eldest son, who claimed the servant committed the crimes. The authorities deemed the case closed, but rumors started spreading that the eldest son was on bad terms with his family. It was then believed that the servant tried to stop him but was killed and framed to be the scapegoat for the murders. The son continued living in the house until he died of old age.

Afterward, there were figures seen in the windows, and screaming and arguing could be heard despite being vacant. Because of the dark history, the mansion became known as the "House of Lamentation."

Eventually, the mansion was transported to the Devildom and became a dorm for the demon brothers.

In Nightbringer Lesson 33-6, Mephistopheles mentions that there used to be another structure on this plot of land before the House of Lamentation was transported here. The structure had rooms that would rearrange themselves every single night.

Common Areas

 * Entrance Hall
 * Living Room
 * Dining Room
 * The Dining Room is connected to the Living Room, as the gargoyles are shown in the reflection of the Living Room's mirror. It is confirmed in the scenery of multiple episodes of the anime.
 * Common Room
 * Kitchen
 * Laundry Room
 * The laundry room is adjacent to the kitchen, as confirmed in the chat The Dream where Leviathan accidentally flooded both rooms.
 * Music Room
 * In the Devilgram Living the Dream, the music room is connected to the dining hall, for the brothers could hear Levi singing in there.
 * Planetarium
 * Library
 * Lucifer's Study
 * Can be accessed from a secret passage in the library.
 * Attic
 * In Nightbringer Hard Lesson 6-12, it is revealed that the attic part of the house doesn't exist yet. So, it is implied that Lucifer probably added it to the house later on.
 * Before being used by Belphegor, the attic was considered Lucifer's private sanctuary where he kept things from the Celestial Realm.
 * Underground Tomb
 * Communal Bathroom
 * In Lesson 42-C, there's an established bathroom order which the brothers decided on a rock, paper, scissors competition. With the exception of Asmodeus, everyone uses this bathroom to take showers/baths.
 * Asmodeus's Bathroom

Bedrooms

 * Lucifer's Bedroom
 * Mammon's Bedroom
 * In the Devilgram Proud Brothers, it's stated that Mammon's bedroom is next to Satan's.
 * Leviathan's Bedroom
 * Satan's Bedroom
 * Asmodeus's Bedroom
 * In Nightbringer Hard Lesson 6-12, Asmodeus states that his room originally didn't have a window as his room is located in the middle of the house. But, Asmodeus really wanted a window in his room, so Lucifer cast a spell to warp the space itself and then created a window.
 * In Nightbringer Hard Lesson 14-14, Luke goes through a door in Asmodeus' closet which leads to a secret exit through a cupboard in the kitchen. Simeon believes that it's Asmodeus' emergency route for when he wants to cheat on his diet since he had one of these secret passages back in the Celestial Realm as well.
 * Beelzebub's and Belphegor's Bedroom
 * MC's Bedroom
 * Their room is located next to the kitchen, as evidenced in Lesson 5-2 when Beelzebub destroyed a kitchen wall shared by MC's bedroom.
 * Their room has its own bathroom, as alluded to in Lesson 4 — when Mammon left his toothbrush there — and in the chat Bath Time with Asmo 1.
 * Lilith's Bedroom
 * Either a reproduction or Lilith's actual room from the Celestial Realm was added to the House of Lamentation by Lucifer.
 * According to the dollhouse replica of the house, Lilith's room is adjacent to Lucifer's.