The Pyramid of the Rings of Akhaten was a pyramidic temple for the Old God. Located on an asteroid orbiting Akhaten, the Pyramid was a holy site for the Sun-singers of Akhet. They believed that life in the universe originated there.
The door to the Pyramid was dead-locked, although the Eleventh Doctor managed to lift it with his sonic screwdriver, finding the door "really, quite astonishingly heavy." There was a second secret door which could be opened by a "secret song", which every Queen of Years knew.
When, at one Festival of Offerings, the Long Song ended, Merry Galel, the Queen of Years at the time, was taken by force to the Pyramid to be sacrificed. The Chorister teleported out to save his soul from "Grandfather".