The door leads you into a hallway that looks like it belongs in some ancient Roman temple. Gone are any signs of the untamed cavern, now the floor is white brick, the walls are likewise, and enormous and intricate reliefs stretch the length of the room, split only by the Doric pillars that reach up to the white tiled ceiling.
You start down the long hallway, but take your time, appreciating the facsimile of civilization even though you're pretty sure the second you cross the threshold again, you'll be dumped back into a cave. As you pass, you find your eyes sliding over the reliefs in the walls.
The images on the walls depict angels at first. Winged angels flying among monstrous creatures with wings-- multi-headed humanoids with animal faces, burning circles surrounded by eyes, indescribable monsters among the recognizable human forms.
Then, it depicts the beginnings of a familiar scene; a winged figure larger than the others being struck by a lightning bolt, the same figure falling from the clouds. Then a city underground, inhabited by monsters.
The mark on your arm glows as you approach the wall.
-->[Investigate?]
-->[Keep moving ahead]