(And yes, by DM fiat everyone sees this in the scrying spell.)
The air in front of your group flickers and warps, and with a faint tearing sound a projected image forms hovering in space, showing you the view from the upmost balcony.
The balcony leads into a chamber just inside the peak of the Horn, a large dome some eighty feet across at it's widest point. The entire inner surface of the chamber is sheathed in a strange copper like material, every inch of which has been carefully worked into images of suffering mortals and spreading pestilence, interspaced with the jagged script of daemons.
Sitting in the centre of the room is an altar, a large slab of green stone stained black with the lifeblood of uncounted hundreds of victims. At the base of the slab is a small basin of oddly colored water, and looming over it is what you can only assume is a statue of Vetra-Kali itself.
The daemon lord takes the form of a six-armed humanoid figure with the tattered wings of a raven. It's skull is equine in form, hideously elongated, and three empty sockets gape from where a trio of eyes should clearly sit. In three of its hands, the statue holds wicked looking daggers, while in the other three it cradles a vial of some kind. The statue is inanimate, but you get the strangest feeling that it is staring at you with its eyeless gaze none the less.
Chained to the front of that altar is something completely out of place in the unholy fane - a large, glittering seal of purest silver, engraved with the sun and light symbols of the god Mitra. It's purity almost hurts to look upon, and the clash between the seal and the surrounding room could hardly be more distinct.
The air in the chamber seems to constantly writhe and crackle with the interplay of deific energies in such utter opposition to each other. Given the crackles of static electricity that you can make out through the scrying, you'd guess there's at least one storm elemental in there, though how many and how large is impossible to tell.
There is also, near the entrance to the balcony, what appears to be a spiral staircase set into the floor, leading from the sanctum down into the lower levels of the temple. It can evidently be accessed on foot from somewhere within.