From the Kickstarter page:
There is only one true city; a place of multiversal trade, cultural exchange, and mixed blood. A place where monsters come to scheme and gods come to die.
Sig: The City Between is the nexus of the multiverse. It's a city connected to everywhere, a refuge for the oppressed and a prize for tyrants. It's a place where culture is at the forefront, with diverse faiths and tongues struggling for space in the crowded metropolis. It's a city of families, both whole and broken.
Sig is also a launching point, allowing fools and heroes to venture into the eternal planes of existence. Each plane is made of concepts, of elements, or of ideals that resonate through the entire 'verse. The planes impose their own Beliefs on Sig, and on the infinite primal worlds beyond.