Terrace (Luigi's Mansion: Dark Moon)
From the Super Mario Wiki
The Terrace is a location in Treacherous Mansion in Luigi's Mansion: Dark Moon. Accessed from the door on the north balcony in the Inner Courtyard, it is an important area explored in quite a few missions of Luigi's Mansion: Dark Moon.
As far as layout goes, there is a giant paranormal portal near the back, along with a fence and various plots of dirts to the left and right. At the south of the Terrace is the door leading back to the Inner Courtyard, and to the south east and west are windows that can be used to look out on the Terrace from the East Corridor and West Corridor respectively. This location is also visited in the game's ending.
In Paranormal Chaos, however, the Terrace is the main destination in the mission. Luigi has to enter the Terrace at the start of the mission to see King Boo open the paranormal portal, then defeat a huge horde of ghosts here at the end to save his dimension from collapsing. The portal is open but cannot be entered until the next mission.
In Stop the Knightmare, Luigi is pixelated here, but then immediately sucked into the portal.
The Terrace is also visited in the ending after the boss battle with King Boo. Here, Luigi has to save Mario from his painting as well as rebuild the Dark Moon, with the help of Professor E. Gadd and the Toads he has met in the adventure. It is also where the ghosts are shown as friendly for the second time and where the group photo is taken before the credits.
In Terrifying Invasion, the portal is closed, so Luigi cannot go back to the boss arena.
The Terrace can also be seen in Luigi's Mansion Arcade. Unlike in Luigi's Mansion: Dark Moon, the Terrace is the area where the player battles King Boo.