Balbol Museum (バル・ボル美術館, Baruboru Bijutsukan) is a Lost Ground located at Σ Hidden Forbidden Exhibition.
After passing through two giant bronze doors decorated with relief images of the eight Phases, a visitor will see a vast facility incorporating almost every known architectural style, including ancient Greek and Roman, medieval Gothic, several Renaissance styles, modern, east Asian, South American, and more. The displays contained within are of archetypes, and look different for each person who views them. For instance, when Kuhn looks at the display for "home", he sees Kanazawa, where he lives and works, Pi sees the fishing village where she grew up, and Endrance sees Mac Anu as it appeared in The World R:1. There are so many exhibits that it would take a lifetime or more to see everything. Beneath the museum is an enormous archive, with hundreds of rows of shelves containing books, pictures, films, and objects of all sorts.
The role of the Museum in the R:2 backstory is unknown.
The role of the Museum in the Epitaph of Twilight is unknown.
After taking over as leader of Project G.U., Kuhn brings Haseo, Pi, Atoli, and Endrance to the Museum as part of an ultimately successful effort to bring all the Epitaph Users together.
The Balbol Museum is likely the Information Storage System used for Aura. It was pointed out that "The World" was collecting every bit of data down to the players emotions in order for Aura, the Ultimate AI, to learn from.