This hall is part of Diocletian's Baths and used to be called the Hall of Minerva. Probably designed originally to provide a concourse area, it is octagonal in shape with four semicircular niches in the corners.

Roofed with an umbrella dome and possessing a central "eye", it was turned into a planetarium in 1928. Today it houses the most important sculptures from the National Rome Museum, all of which have some connection with the baths. It shares an entrance with the other sections of the museum proper, Palazzo Massimo and the Epigraphical Museum of Diocletian's Baths.