Smarter Carissa knew what she was doing, Carissa tells herself firmly, and steps forward into Hell. 

(She does have Resist Fire up because it'd just be embarrassing to be constantly flinching about all the fire in Hell until Aspexia casts Planar Adaptation.)

The fire in Hell isn't even mostly the problem.  Aspexia Rugatonn can feel the weight of Avernus trying to press on her soul, horror and despair and regretting all your choices; before she casts Mass Planar Adaptation on the party, and the pressure mostly eases.

Well, Carissa does regret several of her choices, and she can see how if anyone were in a position to correct her errors right now it'd be useful for her to feel the weight of that regret. 

Anyway. 

Onwards. 

It's a mighty fortress they've arrived to, all blood-rusted iron and seared pitted steel, and lesser devils on the ramparts, looking down at the newcomers with all the scorn their lesser kind can muster.  It stands in the midst of a vast desolation, a volcanic desert with sand of iron and obsidian, from which, in the distance, not really all that far, bursts of hellfire constantly erupt from the ground; the firelight of the plane flickers, but has yet to go out for even a moment.  There are not many petitioners about this place, but in the distance their screaming forms a background sound steadier than the firelight.

The magical Gate has taken them to before the physical sort of gate, polished and unblemished steel that stands in contrast to the rest of the scarred fortress.

Aspexia steps forward and drives her fist into gate, backing it with magic to produce a hollow bang; for the gate has no knocker on it, if you are not strong enough to knock on a door in Hell then nobody in Hell is going to pay you much heed.

"You'll speak for us, for practice," Aspexia tells Carissa.

Right. Makes sense. She wonders if it's really so that every devil in Dis knows her name.  She wonders if they'll be laughed right out of Dis. ...probably not, it's in fact true that she was asked by a devil if she'd settle for three Wishes, and that when she was substantially less valuable. 

Unseen Servants hold the hem of her dress clear of the ashen ground, and she waits.

The outer gates crack open.  Behind them stands a creature like a very tall cadaver, skin shrunk to almost fit the skeleton and skull, but that the skin is itself animated and moving bone.  A great stinger-tail rises from it, and many not-particularly-functional-looking delicate wings of bone, like colorless butterfly wings petrified.

Behind the thing is another, even more imposing-looking gate.

Carissa's new instincts for Hell will tell her that this is an Osyluth, a sort of lesser Security of Hell.  The greater party speaks first, in Hell, and it will be waiting for Aspexia Rugatonn to speak.

"I am Carissa Sevar, called in Golarion Chosen of Asmodeus, come with the Grand High Priestess of Asmodeus to Hell with business for Dispater. We would pass through the gates of this fortress to Dis."

The bony thing turns its head to the evidently far more powerful and Evil soul, with a questioning, submissive look.

Aspexia Rugatonn gives no return sign; only stands beside and to the left of Sevar like an allied mercenary who was not paid enough to speak.

...confusing.

But confusions are not worth resolving, except insofar as they touch upon the interests of the self.

"Do you offer me fee for passage, or threat for it?" speaks its cold rasping voice.

She can't, actually, take a devil in a fight, even a lesser one like this - a caster of her level could probably win this fight if they were an adventurer, but she's not one.

Rugatonn could, though. 

Also they shouldn't have to fight, this isn't the Abyss, that'd be stupid. 

Her voice carries none of this uncertainty and no nervousness about maybe getting unceremoniously stabbed by the first devil she runs into. 

"We're here about Asmodeus's business and will cut down what stands in our way, only negotiating with anything that would otherwise have a true interest in impeding us."

A slight rasping noise that surely is not laughter.  "I did trouble myself to open the outer doors for you, and now you'd have me open the inner doors as well.  Do you pay me for my effort, or tell me to pay it as your due?"

She's tempted to pay, but she suspects she's not supposed to. This isn't Axis. Paying is admitting - something. That she's not very important. And importance is negotiated, and she needs to be important. 

"If you want payment, seek it from someone else, for the story of what you witnessed. We are owed your obedience; open the gate."

The Osyluth reads sincerity in her, and the Grand High Priestess waiting by her side and not contradicting this statement does lend it credit and threat; it obeys, then, and the inner gate swings open.

The interiors of fortresses set to guard Avernus are not so complicated as mortal fortresses, they need not food nor places to sleep, only mazes of traps to also serve as garrison.

Behind the inner gate is the entrance to a dull metal hallway that branches out left and right from the gate's opening.  And a next sentry there, a nightmare of chains linking bladed cogs and jagged gears; a Castigas, a thing stupider than the Osyluth but more dangerous did it choose to fight.

Dozens of pitted lenses angle slightly to point at Aspexia Rugatonn, and then the mass of chains clunks forwards into the left-hand side of the maze, assuming (Carissa's bracer will tell her) the submissive posture of a guide who walks ahead of its superiors.

Carissa feels no doubt, no confusion, no repulsion at the ugliness of the place, though it is, in fact, ugly, not doompunk.

She follows.

They pass through a garrison-maze, made of sharp turns and corners without any curves.  From time to time the automaton-thing presses three floor-tiles in a pattern, or the like, before it continues on.

They pass small garrisons of bearded devils with living, snarling beards below snarling faces, any one of which Sevar might defeat, but which she'd be hard-pressed indeed to handle as a mob.  They are playing dull games to pass the time, more on the level of naughts-and-crosses than any game held respectable in Golarion, though they bring their toothed glaives to respectful yet threatening attention as the group passes.

(Legend says that there was a whole planet of beings like this, which Barbatos sold to Asmodeus and so became archdevil of Hell's first layer.)

At the end of their path through the maze is a vast iron room with a silvery irised gate set into the floor.  Above the gate, a swaying flat circular platform held slightly above the floor-gate by rough-surfaced chains meeting above the platform, connecting to a slightly thicker chain that goes through a pulley and winds about a huge reel.

A brutish-looking horned humanoid with leathery crimson skin, from whose head protrudes a great mouth filled with sharp teeth, waits about the reel.  It's a Marzach, Carissa's bracer will tell her, and smart enough to be a wizard albeit a mediocre one by the standards of Golarion.

Like the guard of the entranceway, it takes one look about Aspexia Rugatonn and then waits to be spoken-to.

Then she will say again, "I am Carissa Sevar, called in Golarion Chosen of Asmodeus, come with the Grand High Priestess of Asmodeus to Hell with business for Dispater. We would pass through to Dis."
 

"And do you offer me fee for passage, or threat, as I stand here above and lower you down?"

This is just frustrating. She bets Axis has one guard to bribe, instead of a whole line of them. "I am owed your service, and you'll provide it."

Again it glances at Aspexia Rugatonn not denying this, and then goes to crank the floor-door iris open.

These beings are very regular and predictable once you have a small amount of experience with them!  If you have any experience dealing with free-willed mortals it's a relaxing change of pace.  It makes you wish that all the workers on your project were this easy to predict!

The platform, notably devoid of any safety rails, or anything to hang onto except those rough chains, sways and tilts in the heated breeze that rises up from the opened iris, even as the Marzach goes to wait by the chain's reel.