You proceed up the long flight of stairs to the first, and lowest, entrance to the temple proper. The landing you arrive on is not particularly adorned or ornamented, and at a guess you would imagine this floor was reserved for the less senior members of the cult.
The landing at the top of the stairs was clearly meant to be guarded, as a guardroom on each side covers the entire approach by means of half a dozen arrow slits apiece. Now, though, they are empty and abandoned, as is most of the level. As you make your way inside, it becomes progressively more obvious that hard fighting took place here. Old blood stains, chipped sections of masonry and the distinctive blast patterns of arcane spells are everywhere... though there are no bodies or leftover equipment.
Exploring the level yields no encounters with sentient life, and is quickly resolved. This floor of the temple appears to have been mostly devoted to secular activities and low-ranking accomodation. There are eight different bunk halls, each with half a dozen or more old beds that have mostly fallen into disrepair and rot. There is a smithy here, and a reasonably sized tavern. Beyond that, there are four things of note.
The first is an old fountain in the centre of the main hall, wrought in the likeness of the skeletal boatman Charon. Water flows like blood from between it's ribs and collects in the hull of its morbid barge. Despite the years of neglect, the water appears perfectly fresh and untainted.
The second is a storeroom, where the cult evidently kept their provisions. The food and drink are gone now, but there is still one thing here - the corpse of a Minotaur, pinned to the floor by an ornate spear that someone rammed through its chest with incredible force a long time ago. Despite the passage of years, the corpse is perfectly fresh, preserved by whatever enchantments the Sons of the Pale Horsemen used on their supplies.
The third is some kind of throne room that adjourns the barracks. The walls in here are adorned with scenes of daemonic victory over a horde of broken angels, and the throne itself has a small inscription on its base - the abyssal word 'yah'.
The fourth is an alchemical workshop of some description. Most of the delicate supplies are gone, and the books of instructions are jumbled up and disorganized, but on a workbench in the centre of the chamber is what appears to be a golem of some description. The gangling bronze humanoid figure has clearly been the victim of some violence, but you can tell at a glance it is probably not beyond the realms of repair, provided you could find the right tools. The Sons evidently thought so too - chips of bone and sprays of old blood around the room explain why they didn't manage to complete the repair works.
Finally, there is what was obviously some kind of trophy room. A dozen display cases and stands have been broken open and looted around the room, leaving only the accompanying inscriptions to tell what might have once been held here.
Laedrissa the beautiful, who believed she need not honor her promise to us.
Markan the Golden, draconic protector of Losswyn. He slept then and now sleeps forever.
Kallister feign, an illusionist too clever to keep his head.
Lazarus M. Who mourns for you now?
King Croc, 23ft from snout to tail, delicious on a spit.
Iris of Ghastenhall, dead of a broken heart and a poison dagger.
The great serpent of Korokunga, slain for its venom.
Lord Halifax the Just, hid in his castle and hoped we had forgotten. We hadn't.
Snorri Five-axe, died on a sixth.
The ears of Lord Kallerrian. If only he had sense enough to listen.
King Gorgon Sakkathet, unbeatable in battle, careless in choosing his cup-bearer.
Ergun Nygma, the third scion of the House of Hyral, the second greatest swordsman in the land, the first to die.
There is a staircase leading on upwards near the rear of this floor. You cannot hear anything coming from the floors above, but that might not necessarily make them safe.