Anything that evolves piques my interest, religion included. I find many mythologies fascinating, but in particular I am interested in the older mythologies, the "stem-religions" if you will, such as Sumerian religion.
Many religions through time has placed deities right here on earth, in flesh and blood, as emperor "god kings", and in Sumerian religion this is very prevalent as well. Deities and historical figures blend and intermingle. The Sumerian list of kings consists almost entirely of deities in the beginning of the list, with some ridiculous longevity-claims attached to each ruler, in particular the first five (there's claims of lifespans lasting over 40 000 years)
I also like how ancient Sumerian cities would be dedicated entirely to one deity or another, giving whole cities a certain personality - even a certain purpose. This pattern has developed independently in later civilisations throughout history, but there's something remarkable and unique about these *very first* examples of this strange social dynamic.
Prior to city states and god-kings, these populations were nomadic shepherding tribes, foragers and fishing communities, and they very likely worshipped personified stars/celestial bodies, for example a very obvious candidate, the planet Venus, who became personified as the goddess Inanna as early as 5000 BC, a deity of duality, love plus war, a reflection of it being the evening and morning star
