The Orrery Chamber is a location in the castle on Shandor Island. The chamber contains another device built ahead of its time, an orrery that is aligning dimensions.
After capturing a Imprisoned Juvenile Sloar, the Cult of Gozer then imprisoned it within a Ghostworld pocket at the heart of an orrery. For decades, the Sloar guarded the orrery and provided the Cult with Black Slime against its will. The orrery itself is a device typically used for predicting planetary alignment. In this case, Shandor's version has a different function: aligning dimensions. A pool of Black Slime near the orrery's base powers the machine. Several orbs rise and fall as the center spins to align the multiple dimensions. The movement of the orbs stabilizes the interior structure, as well. The motion of those devices seems to be generating some sort of energy related to the alignment process.
The Orrery Chamber is located at the rear of the Slime Laboratories. A platform on the ground floor of the lab can be taken up one level. From that point, a stairwell leads to the entrance to the Orrery Chamber.
Rookie used the Slime Tether to anchor the orrery's orbs. However, this caused the room to fill up with Black Slime. The Ghostbusters ascend to higher ground to witness the orrery's collapse and the Imprisoned Juvenile Sloar rise from the slime. After the Sloar is defeated, the island begins to sink. The Ghostbusters retreat back to Marine Ecto-8.
Ray Stantz speculates the Orrery acts as an extra dimensional portal that draws energy forms in and out, filtering out what the Cult didn't want, like an evil strainer that just lets evil in and shields out the good.
The main ability of the Orrery Chamber is to align dimensions and harvest Black Slime from the Sloar. Egon Spengler notes the readings emanating from the chamber are as big as when he, Ray Stantz, and the Rookie crossed over at the New York City Public Library.