Kroms steps forward and feels the cold stone of the mountain the fortress is carved from. Hewn from gray stone, the fortress is bereft of ornamentation or artistic flair. Doors are likewise made of bare stone, with iron handles and hinges.  A moment later and an entrance is made and you step into what appears to be a guard room.

Tunnel ceilings are 10 feet high and flat. Room ceilings are 15 feet high and vaulted.  

This room is heated and illuminated by braziers of glowing-hot coals. Visible on the west wall an iron lever, and a heavy iron winch.

A floor-to-ceiling iron cage in the middle of the room contains an elevator shaft with chains running up and down away from it. The chains are in constant motion, and you hear loud mechanical noises higher up the shaft and farther down as well. A double door is embedded in the middle of the east wall. Air enters the room through a row of four arrow slits in the south wall.

As you enter, Chill notices something right away.  In the southeast corner someone is trying to avoid detection. Despite their effort they cannot stop their cold breath from being visible. 

Krom knows duergar enough to know that they have the ability to turn invisible.  Someone is there, in the corner.

To the north the open passage leads to a set of doors and open passages that lead to the right and to the left.

Now that the group were inside and no further scouting seemed immanent, Gorrah grudgingly takes the opportunity to fly her way over to Rhogar and take refuge in the Dragonborn's hood as said sorcerer gave the room a cursory look. "Hmm... Strange. Broken ties to their kin or not, I half-expected at least someone to be on vigil here, ready to thwart intruders. But mayhaps there was truth to your assertion before, Master Krom, and that some madness had taken them over." He'd say as he'd at least begin making his way to the northern exit if none stop him. "Or perhaps they've already run to alert others. If so, we best hurry." 

Krom stops Rhogar as the dragonborn starts walking to the northern passage. "We are not alone Rhogar." 
"Show yourself duergar, we know that you are here." says the dwarf pointing towards the southeast corner as Chill informs the group.

 Kazri moves to the eastern double door to block it from whatever might be in the room.

Chill quickly informs the group of what he sees in the corner.  "Someone is there, I can see their cold breath."  He then stations himself by the open passage to the north to keep watch has Krom moves forward to confront the likely duergar hiding there.

As Krom approaches the corner the Duergar shows himself

"Ah, yes!  Who are you! Why are your here?" he challenges.

"We are the Fellowship of the White Cloaks, I'm Krom Firebeard, Smith of Moradin." Krom takes a step forward "We are here to stop your warlord and your dragon from ravaging the Ten-Towns. Where is he and where is the human wizard you captured a couple of days ago?"

Though at first skeptical, the fact that two of his compatriots seemed certain of the threat was yet enough to keep the Dragonborn from at least taking beyond the doorway to the north. He would however gesture with his head for Rekuberk to at least keep an eye on the entryway, while Rhogar focused more inwardly like the others. "So it was true.." He murmurs, having yet been taken aback in seeing the Duergar appear from nothing. Once the Dragon is brought up again, on the other hand, shock is burned away by restoked fury. "And do not 'play ****', as they say on the docks of Neverwinter. Our patience is thin, and so too shall your remaining time on this plane if you do not answer his questions honestly." He states as electricity began crackling and dancing across his teeth.

If a check is needed/desired:

Kazri stands by the eastern double door. She is ready to engage the Duergar if he becomes hostile.

The duergar throws his hands up.  "Too late to stop the dragon.  Xardorok is insane, or at least paranoid and he just unleashed the beast.  I long to be rid of Xardorok.  Help us over throw him!  I can take you to Grandolpha Muzgardt who is trying to replace him."

Chill, Krom and Kazri have high enough passive insight scores to see that the duergar speaks honestly.

Rhogar lets out a throaty growl and took a step closer to the Duergar. If, however, the more insightful of the group speak up on the Duergar's behalf, the Dragonborn exhales a frustrated breath through his nose and steps back, and leave further discussion to the others in distrust of his own restraint. For the moment. Gorrah pokes her head out at that moment, and took to keeping a weathered eye out for any other Duergar in hiding that might yet sneak past the others. 

Krom takes another step towards the duergar "Duergar created that dragon using that demon-infused crystal, do you not have a way to control it or recall it here?" says the dwarf lowering his warhammer "Our quest is to help the people of the Ten-Towns, if Grandolpha Muzgardt and you lot stop to raiding, harassing the Dale and if return peacefully to your caves in the Underdark I think that we could consider your proposal." Krom pauses for a moment "But I will have to speak with Muzgardt first."
The dwarf asks to the rest of the group "What do you think? Duergar are crafty people, but this one is saying the truth about their intentions."

"If this person speaks the truth, I believe that is the best lead we have so far." Kazri lowers her stance.

Chill listened and watched from his post at the hallway.

"I say we follow him.  This leader person maybe has answers."

"Follow me then." the duergar says. He moves past you and down the open hallway that Chill watches.  He stops at the intersection and looks both directions.  Satisfied by what he sees, or doesn't see, he moves to the east to a set of double doors and opening them he ushers you inside.

Three braziers heaped with glowing-hot coals illuminate and heat this long hall. At the eastern end is a hexagonal stone table surrounded by six stone chairs. Seated in the chair facing the door is a haggard old duergar with long black hair streaked with ribbons of white and fingernails like shards of iron. She is devouring a hearty buffet of cooked meats, mushrooms, and strange Underdark fare. Lurking next to her is a small mechanical dragon made of a shiny black substance.

Hunched over a hot stove in the west side of the room are three duergar cooks. At the sight of you, they drop their utensils and reach for their weapons, but the old duergar says something in Dwarvish that keeps them at bay.

"Dreck, who do we have here?" She asks. Dreck seems to be the name of the duergar you have followed.

"Potential allies Grandolpha Muzgardt. They have come to Sunblight to stop Xardorok and the dragon he unleashed." Dreck answers.

"So, you have eh?" Grandolpha says turning to you "What say you then?" She asks you "Xardorok is a fool, perhaps we can both get what we want here?"

As the duergar leads the group within the fortress's corridors, Krom, not completely trusting his race's ancestral enemy, keeps his hand close to hammer's grip. Seeing that the duergar does not lead them into an ambush, the dwarf relaxes a little bit.

After Dreck's introduction and Grandolpha's inquiry, Krom takes a step forward and after eyeing for a moment the cooks, addresses the old duergar.

"He speaks the truth" says the dwarf indicating Dreck "Our Fellowship's goal is to help as much as we can the people of the Ten-Towns in this dire times. Your warlord, your soldiers and your dragon, in this precise moment, are ravaging their land, we travelled far to stop this madness." Krom pauses a moment to let sink his words "If you swear to stop looting, harassing the people of the Ten-Towns and to let live them in peace, then, you can consider ourself allies against Xardorok."

Kazri stays by the double door, she will stand guard by it. Meanwhile, she will also keep an eye on the cooks.

Perception: 16 (for movement outside, if needed)

Rhogar watched the Duergar passed by with a heated glare, but otherwise held his tongue and restrained the impulse to strike. A sidelong glance is given to the others after which. Yet without a word, he fell in line with the procession. At the intersection Gorrah looked about ready to part ways with the party, seeming curious at first at what laid down the other path, only to hesitate and look to Rhogar. Following some short and unspoken exchange, the two then nod in unison and carried on after the others.

Soon enough, the party meet Dreck and her crew, and though a wary himself, Rhogar stood by Krom ready to subtly dismiss any magic from the Duergar. "... What exactly is it that you want, Grandolpha Muzgardt? Beyond clearly the removal of this Xardorok."

Chill grinned at Rhogar as he passed by and gives him a wink.  He takes up position at the back and looks around as well as they move down the corridor.

As they others pose their questions, Chill can't help but ask one of his own.  "What's your angle in this?"

 Grandolpha smiles.  "I am the grand dame of the Muzgardt duergar clan, and have just recently arrived at the fortress after being invited here by Xardorok. He has been eager to take a fourth wife and has had his eye on me for many years. I have been entertaining Xardorok’s offer but haven’t agreed to anything. The mechanical pseudodragon was a gift from Xardorok, designed to win my affection. Xardorok has programmed his chardalyn dragon to follow a prearranged flight plan which my people can show you.   He is also capturing Underdark monsters, which he plans to unleash upon Icewind Dale. He has also captured a myconid sovereign and is using its spores to reanimate corpses. I have begun plotting with disenfranchised advisors and warriors in his ranks to overthrow him when the moment is right. Given time, I think I can turn most of the Sunblight duergar against Xardorok. Several of them have already pledged their loyalty to me. You could help accelerate that.  I have no stake in Xardorok’s plot to conquer Icewind Dale and have done nothing to help or hinder his efforts. But he is losing control and needs to be removed.  My angle, is to expand my own area of control.  But I have no interest in conquering Icewind Dale.  Help me and the troubles his people cause to the people of Icewind Dale will stop."