The Astronomers

They worship in ziggurats of yellow brick.  Inside of these are thousands of tiny, brass plaques.  Each of these is a binding ascertained through the study of extinct constellations.  On each is written a required offering and its reward.  The reward is not described, but a destination given in time and space for its retrieval.  An offering might be anything from a copper coin to a life.  A reward might be anything from wealth raining from the sky to a quiet voice that answers three questions.  The times of granting run from long past to far in the future.  It is possible that a visitor exploring the ruins of the Astronomers can still find some of these that are yet to come to pass.  But some scholars warn that doubling an offering will break a binding, resulting in chaos, and it's hard to know what those in the past have offered.