In the Slavic folklore, Baba Yaga is a witch who flies on a giant mortar, kidnapping small children. Also, her home is a cottage that walks, albeit on chicken legs traditionally. The phrase "baba yaga" translates from Slavic to "witchy old hag."
Baba Yaga Castle is located deep within the Amazon basin, at the center of a cavernous ravine 2,000 meters underground. The cave features little else other than rocky terrain but the surrounding areas outside are filled with abundant and dense vegetation of the rainforest. 
Baba Yaga Castle, taking after Arachnophobia's leader, Arachne, is in the shape of a giant spider carrying a castle. The main entrance is that of the spider's head, which is a round red orb with four dotted eyes; if not for the extra eyes, the head resembles the mask worn by most Arachnophobia members. There are also old unused tunnels in the rainforest that lead to the castle. The eight legs are individual towers holding a Demon Tool known as a Lock. On the spider's back is the main castle building, that has large turrets and battlements. The inside of the castle is built in quite an old-fashioned style, with stone walls and archways (all with a spider theme) in the long winding passageways.
Around this perimeter, countless Sensor Threads have been placed in the Amazon rainforest, forming the shape of spider webs. To monitor all of these sensor threads, Arachnophobia has multiple members in Baba Yaga Castle's Security Operations Room to look at a map of the Amazon basin, with Baba Yaga Castle in the middle of this map. Should any sensor thread be tripped, the thread appears on the map as a blinking dot (light blue arrow and yellow skulls in the anime).
In cases in which multiple threads are tripped, Security then may turn on alarms throughout portions of Baba Yaga Castle to warn Arachnophobia members to take appropriate actions, which may include leaving the castle to arrive at the location of that threat. These threads therefore make it difficult to approach Baba Yaga Castle. In addition, these threads are rearranged every few days, such that should their locations be revealed by moles within Arachnophobia, such intelligence would be outdated very quickly.
In the anime, it is also explained that various traps are set up on the outside of the castle to deter people from finding the location or killed to conceal the location. There's also various Tracking Spiders around the forest for Arachne Gorgon to witness activities herself.
- Towers 1-8: Each of the spider-shaped castle's legs are towers, each hiding a Demon Tool known as Lock, in which act as the magical-based security system of Arachne's Spider Queen Room.
- Smoke Room:
- Giriko's Room: A large room and the dwelling quarters of the Enchanter, Giriko. However, due to his activities, it is an constant mess to the point he requires it to be clean ever half-hour.
- Asura's Room: In the anime, upon Arachne persuading him to join Arachnophobia, Asura is housed inside a bedroom, where he is served Arachnophobia agents for meals. The room is later modified to house the Morality Manipulation Machine to channel Asura's madness wavelength to project out of Baba Yaga Castle.
- The castle's design, most specifically the center portion in the spider's back bears a striking resemblance to Pieter Bruegel's artistic representation of the Tower of Babel.
- ↑ Soul Eater Manga: Chapter 26
- ↑ Soul Eater Volume 7, Yen Press English translation: Page 195
- ↑ Soul Eater Manga: Chapter 46
- ↑ Soul Eater Volume 7 Yen Press English translation: Chapter 27, Page 160
- ↑ Soul Eater Volume 12 Yen Press English translation: Chapter 48, Page 164
- ↑ Soul Eater Volume 13 Yen Press English translation: Chapter 49 Page 7
- ↑ Soul Eater Anime: Episode 45
- ↑ Soul Eater Volume 12; Chapter 48, page 139
- ↑ Soul Eater Volume 12; Chapter 47, page 115
- ↑ Soul Eater Anime: Episode 39
- ↑ Soul Eater Anime: Episode 40