Eientei

Eientei, also known as the Eternal Mansion, is a prominent location in the Touhou Project series. It serves as the primary residence of several characters, including Kaguya Houraisan and Eirin Yagokoro. The mansion is depicted as a fantastical and ever-changing place, often described as existing outside of normal time and space, making it difficult to find and navigate. It is surrounded by a vast bamboo forest, which also possesses peculiar properties, further contributing to Eientei's elusive nature.

The mansion's inhabitants are known for their immense power and knowledge. Kaguya Houraisan is an ancient princess banished to Earth, possessing immense magical abilities and immortality. Eirin Yagokoro is her loyal companion and a skilled pharmacist and scientist, equally immortal and wise. Their presence at Eientei is central to many storylines within the Touhou universe, often involving visitors seeking their aid, knowledge, or simply stumbling upon the hidden estate. The nature of Eientei itself reflects the timeless and somewhat detached existence of its residents, making it a place of mystery and wonder within the series. It is a location where the mundane rules of the world do not apply, and where ancient secrets and powerful beings reside.