You do not find the hoots.
You still have plenty of glowstones (Seriously, they last months), so you're set there. Given the oppressiveness of the darkness, you strap a few extras to your packs and armour, so everyone's got three. One behind them, on their packs, one strapped to their belts, and one being carried on a neck strap, like usual.
The darkness does flicker as you move northwards. Perhaps more worrying than finding out whatever is making the faint hoot sounds is hearing the hoot sounds stop. It means it's much less likely to be something natural, something that just makes sounds as water flows or air blows or steam hisses or something. The hoots don't cease immediately. You're marching through the vertical fissure for about a full kilometer before they stop. You stop too, and wait for them to resume. They do not. You try retreating a bit.. and the faint sounds don't begin again. Nothing left to do but to move forwards.
Ahead, there is a clear chokepoint as the passage narrows. It's not narrow enough to block passage, but it's now narrow enough to be blocked by one person. Above, there is still no roof, simply the harrowing blackness and narrowness of the vertical slit to eternity. ..Although, over here the darkness doesn't quite dance the way it does further south. Instead, it's a still darkness, now that the hoots have ceased, only lifted by your footsteps. It's empty.. or silent. Sessha is concerned something is watching as the party marches through the narrow darkness.
Eventually the narrow fissure comes to an end, and begins widening, leading to a series of broken steps leading into a shelf upwards. Each step is about fifteen feet high, so you need to lift each other over it carefully, two people scaling while someone remains on watch. After about six or seven great steps, a roof appears from above, creating an alcove at the end of the steps.
Inside the alcove is perhaps a proper room. There are signs of finished stone, and two very grotesque statues in the corner, dripped on with minerals and utterly fused with the floor. They're clearly worked pieces, but here and now they only form indistict somewhat humanoid-ish forms, taller than they are wide or deep. The corner contains two basins of water, one clear and one with a faintly visible movement inside it. They're formed by the stone being carved into the floor of the rock. Overall, there is enough room to camp here, although you can't have the tents, and the open space is open to the top of the flight of broken stairs.
Examining the room more closely, there are no other visible entrances, although there are two large cracks in the wall, one leading up and west, and the other leading about due east, at floor height and horizontal. There are also several large blocky objects in the middle of the room, more carved stone that may have been taken from the ceiling long in the past. As for the ceiling, it looks pretty solid now, the chunks were carved out and turned into some indistinct shape long ago.
Base Camp, where everyone fell down to. Two exits, north and south.
North of base camp: Empty fissure -> Giant Stairs -> Alcove Camp
South of base camp: Dancing Darkness ->