The Threat From the Deep
The cosmology of this world is similar to that of vanilla D&D. There exist many planes of existence, all relative to the Material Plane, the one to which Elos belongs. There are elemental planes of Earth, Air, Fire and Water, as well as transitory planes such as the Astral Sea, the Plane of Shadow, and the Ethereal Plane. And of course, there also exist the Higher and Lower planes. The Higher planes are the homes of untainted creatures – what we would call Angels, Devas, and even the Gods. The Lower planes are those that are suffused with corruption – the Hells and the Abyss. They are home to demons, devils, and the dark Gods.
Religions vary across Elos, but the Gods are not immaterial – the presence of the divine (and the Tainted) is very much real. In Gardania, churches to Erathis, Avandra, Kord, and Pelor (the father god, the mother god, the storm god and the healing god, respectively) are commonplace. In the darker corners of the world, cults and churches of Tainted powers such as Torog, Zehir, and Vecna might also be found. There is also the concept of ancestor worship among Dwarves and Elves. Exotic races and cultures from beyond the Southern Sea might have their own deities as well – though they are sometimes worshiping the same gods by other names, the existence of powerful demigods and other entities is certain.
All of this cosmological knowledge is common knowledge to the people of Elos – it is general knowledge about how their world works. If you pray to Zehir because your neighbor stole your cow and you want to curse him, very real, very bad things will happen – probably to both of you. By the same token, clerics and priests are granted tangible power by their gods. Magic is both real and fairly accepted in Elos, and even commonplace in parts of Gardania, especially Inverrin.