Ah, if only I had the Soul Eater ability... I search the corpses for items and diaries...

You are looking for diaries, but you find nothing; only battle can reveal what happened here, and demons are not very interested in writing treatises. Arrows, all the demons were killed by arrows, there must have been snipers here, an ancient order of elves, which was resurrected by the elven kings as a tribute to tradition.
Actions?

I take out my sword and cut down the Losso... I get up... I peer into the darkness... everywhere there are rats and cobwebs... I continue on my way, occasionally looking back!

You walk and see a light in the distance; you enter a room, everywhere there is light, then the paths diverge, 2 entrances, actions?

I gather my last strength to cast a flight spell. If it doesn't work, I'll go through the ancient part of the Temple, approximately towards where there is a passage to the trident.

The flight didn't work, but maybe the artifact is hidden under the altar, and it can be pulled out from here without any particular problems? Actions?