The queencell was a chamber present on Borg cubes, though it was not where the Borg Queen lived. It could be hidden behind moving bulkheads.
By the 2380s, these chambers had come to incorporate a spatial trajector, a transportation technology with a theoretical range of 40,000 light years, which the Borg had assimilated from the Sikarians. They were reserved for the Borg Queen in the event of an emergency.
The derelict cube called the Artifact had a queencell, which was hidden from its Romulan owners with the knowledge of Borg Reclamation Project director Hugh.
In 2399, Hugh took Soji Asha and Jean-Luc Picard to this queencell and used it to help them escape the cube for Nepenthe.
Later, Seven of Nine used the queencell to activate the Artifact and the Borg drones still in stasis aboard. (PIC: "The Impossible Box", "Broken Pieces")