Presumably the seal also placed an illusion or something. Ruby will just explore this chamber and wait for Erandur to do his thing.

Indeed. Erandur starts casting some complicated magic on the graven image, and seems wholly engrossed in this for a while.

Ruby dismisses the Dremora, then, since it seems like this will take a bit. Which makes sense, a seal you could just unmake over a few minutes is basically useless.

...which brings the question of how Erandur can do it at all. It doesn't seem like he's brute forcing it or trying to do the magic equivalent of hitting it with a battering ram, so that's curious. Ruby has a little hypothesis here and depending on which half of the hypothesis is true he might just be in a lot of trouble.

He hopes not.

"It is done," says Erandur at the same time as the graven image—and the wall behind it—suddenly turn translucid and, as demonstrated by Erandur walking through them, intangible. "Be on your guard; if my guess is right, the more the Miasma seeps out of the temple the more people will wake."

"The Miasma" is probably the low-hanging purple mist that seems to permeate the place and that is, indeed, seeping through the no-longer-solid wall. Ruby resummons the Dremora, casts Stoneflesh on himself, then conjures a bow and a quiver of arrows—he found out recently, while hunting in the wilderness, that he's passable at it, probably courtesy of his past life, and this here seems like a good opportunity to practise more. The staff he holds Telekinetically; if he's not doing anything particularly complicated with it he can just make it hover after him at a fixed distance while paying barely any mind to it.

They're in a hallway that seems to form a spiral around the center of the tower. To their left there are stairs going up, but Erandur goes right instead, and the path consists of flat landings followed by stairs going down. The wall between them and the hollow inside of the tower is broken by grates that permit one to look into it and down a couple of stories, where they can see a circular chamber with a tall altar. On this altar there is—something—protected by a circular energy field, and Erandur points it out to Ruby. "I believe that is the artefact I mentioned, the Skull of Corruption. If we can reach it, I will be able to disable the wards around it and destroy it."

Will you, now. You continue to know a suspicious amount about these people.

Nevertheless, there's no point in remarking on it; if Erandur turns hostile Ruby will deal with it then. For now he'll instruct his Dremora to scout ahead, since it's going to be their tank for the likely coming fights.

They advance slowly, counterclockwise, past a few doors to their right that presumably lead to the various rooms that probably line the walls of the tower.

After walking a little bit, they see two orcs sitting on the floor, looking groggy and confused.

And naked. It seems that they have also not been spared Sanguine's prank.

"...oh, of course it affected everyone in the temple. You know, I bet Sanguine would love it if we could solve this with less fighting and more fucking."

The orcs hear him and immediately jump to their feet, trying to get to attention despite their grogginess. "We mean you no harm," Erandur says, but it's no good; they don't even say anything, they merely attack.

With their bare fists. And no armour. And no magic. Which means the Dremora gruesomely slices through them with its greatsword. "Weaklings," it growls.

"Rrright, then," Ruby says, feeling queasy and deciding he will stop looking at the bisected bodies right about now. He did not get any more used to the smell of blood since last time.

At least it's not burnt flesh.

Erandur seems—mostly unaffected by the gore, actually.

"Damn it," he swears after walking past them and noticing that the doorway that continues their path down seems blocked by an energy field not unlike the one surrounding the Skull of Corruption. "...we do not have enough time for me to dismantle this, the cultists and the orcs will all wake if we wait that long."

Ruby walks towards the barrier, gingerly dodging the pooling blood, and hums thoughtfully as he examines it. Then he points at the floor. "Not all of them. Seems like this barrier also traps the Miasma in, so whoever is on the other side will probably not wake. Right?"

"...good observation. Though the grating into the hollow center of the tower would still allow some of it to escape, even if the Miasma is heavy and it would take a while."

"Sure, which means we don't have forever, but we do have at least a while. Unless you have a better idea."

"Well, there is... one possibility."

"From your hesitation I take it that it's not an obvious unalloyed improvement over the time-consuming solution."

"It is not," he admits. "There exists a concoction called Vaermina's Torpor which can be drunk to inhabit someone else's memories for a time and then synchronise some aspects of it with the physical world. You could use that to use someone's memories of the other side of this barrier and then transport your body there and disable it from the inside."

"Something tells me that that 'you' in those sentences was not a general-you."

He sighs. "No. It uses Vaermina's magic as a key component, and so it does not work on anyone who follows another; in fact, it would be actively poisonous. And since I follow Mara, I cannot safely drink it."

"You realise how this sounds, right? Especially given that—well, you seem to know rather a lot about this place."

"Yes. I suppose there's no use in hiding it. I used to be one of the cultists here, decades ago. I fled at the time of the attacks and have spent the time since then trying to atone for my sins. Mara herself sent me back here, when the nightmares started, and I believe it to be her plan for me to undo these wrongs."

"Orrrr, and don't get me wrong, you sound like a swell guy, but we've just met, and for all I know you are still a priest of Vaermina and you just want my help with waking the others."

"...yes, I suppose that's a reasonable conclusion."