yeah it's the new BtS ultra-early religious UN. it's pretty nifty but also really bizarre. the civilopedia has it listed under "beyond the sword concepts" as the easiest way to find it i think. main thing to remember is, it will always be the state religion that original builder had when it was created (whether that was you or whether you captured it, i don't know, but it doesn't matter). it doesn't convert with you like spiral minaret does, so keep that in mind.
it adds some funky new stuff to the game! i can't think of any quick guides to it offhand. there are lots of threads about it, but naturally most of them are people complaining about what they'd change about it, same as a lot of threads around here *giggle*.
welcome to CFC, good luck and have fun!