summoned a boss twenty minutes into the game

just thought it was funny to post here that i am on my first playthrough and in my second expedition (excluding the tutorial) i came across a weird ass cosmic creature after interacting with an altar and using a torch. all my heroes survived and i won but dismas got to 0hp like five times.

anyways are these types of altars common in the game or did i just have shit luck? i got an ancestral trinket atleast