Trinity Festival

Cosmology and the lay out of the space that surrounds Exandria is quite the mystery. Past scholars have looked into the night sky, wondering what fire burned so bright that it painted the sky when the sun set. Past scholars have pondered if there are other worlds out there, like Exandria. What were they like? Did they move and act like the creatures of this world? The existence of the Outer Planes complicates this. Did those other worlds have their own Feywild? Do the gods' reach extend to those other worlds?  Some arcane practitioners attempted to explore the inky black, either by teleporting as far as they can see or simply by flying out. Needless to say, they all perished incredibly mute and twisted death, most of the time by affixation or pressure build-up. 
Technology or magic are not yet at a point where that frontier can be explored, and as such, many mythologies have sprung from this gap in knowledge. Religious folks believe the stars to be the gods' tears. Others say that the brightness are old gods, shining down on the world of Exandria. Even beings who take residence in the sky have their own legends. Cloud Giants speak of an ancient sub race of Giants that traversed the night skies, calling them Celestial Giants, though of course there are no records of those to be found in most libraries. 
Because there are no concrete answers about the celestial bodies that exist beyond the scope of Exandria, many cities have created their own festival and beliefs centered around those bodies. Of course, the great white Catha is associated with the power and good will of the goddess Sehanine, the Moon Weaver. Ruidus, on the other hand, is thought to be an old affect from the Betrayer Gods, long before the Age of Arcanum or the Calamity. 
One such festival, held in Brussendar in the city of Oaken, focuses on the relationships between these celestial bodies. Once every 50 years or so, Exandria, Ruidus, and Catha align to be in a perfect triangle in the night sky. Catha, associated with the Moon Weaver and Mount Celestia, and Ruidus, associated with Carceri. Exandria representing the Prime Material Plane. The festival is to celebrate the balance between the three realms. Though some believe that the establishment of the Divine Gate has caused some problems in this balance. 
Others believe that due to the raw power of the alignment, gates around the world open up. Where they are, or where they lead, is unknown. But there are whispers of things that come through at that point and not at any other time.