The Scarlet Devil Mansion (紅魔館 Koumakan), also referred to as the Scarlet Manor or Scarlet Mansion, is a European-style mansion owned by Remilia Scarlet. It is located on a ridge on the edge of the Misty Lake. From the outside, there are scarlet-colored windows, but there aren't many windows because of the nature of its vampire residents. There are plenty of rooms without windows at all, too. There is a clock tower on the roof, but the bell on it only rings at night. The inside of the mansion is much larger than is apparent from the outside. This is due to Sakuya Izayoi's ability to manipulate time and space.
The mansion's owner is Remilia Scarlet. Patchouli Knowledge, a friend of hers, resides in the library, while Remilia's sister, Flandre Scarlet, is not allowed to leave the mansion. Hong Meiling acts as the gatekeeper, but is frequently overpowered by many characters. Some time after the events of Ten Desires, a number of hobgoblins were hired on as additional help.
Many fairies are employed by Remilia Scarlet as Fairy Maids in order to clean the mansion, and they're overseen by the head maid, Sakuya Izayoi. The maids don't appear to be very useful, however, since they are just fairies. According to an advertisement in Bohemian Archive in Japanese Red (Cirno's interview), maids are provided with three meals a day and uniforms, but no paid vacations, breaks, or afternoon naps. However, unofficially (in terms of the mansion's policies), the fairy maids are free to do as they please, and another employee gatekeeper Meiling is known to take afternoon "siestas" (which is either close enough to a nap, or an excuse to cover up that it is an actual nap). The advert shows the mansion is open to hiring other beings as maids, and Sakuya has indicated in the vampire team ending in Imperishable Night that if she were to train a successor, it would be human, but currently Sakuya is the only human maid at the mansion. The maids are free to leave and return to regain their posts, but despite the fickle nature of the mistress, their lives are comfortable and most end up staying.
The magic library in the mansion's basement is said to be the largest in Gensokyo, but as it is not open to the general public, it's relatively unknown what kinds of books are in there. Hieda no Akyuu suggests that there are very rare magic books, and there are also many books from the Outside World. Certainly, unconfirmed to Akyuu, at least some books are in Esperanto, some were written by Patchouli, and some are dangerous to even touch. Remilia created a swimming pool in the library after the events of Silent Sinner in Blue, but this is not intended to be a permanent fixture. Koakuma resides here and serves Patchouli. It is unknown if she's the only little devil at the mansion, or if there are others.
Events are quite commonly held at the mansion, but as there is usually no previous notice of them, the residents are the only ones that attend. Various events are depicted in Strange and Bright Nature Deity, and it seems that Marisa Kirisame is a frequent visitor. Once event for example is, as part of Remilia's plot to fly to the Moon in the Moon Rocket, the mansion held a publicity event during Silent Sinner in Blue to promote it, inviting pretty much everyone from the main cast of characters. The incident in Embodiment of Scarlet Devil in 2003 made the mansion well-known to humans, and because of this, many characters throughout the Touhou Project will visit here.