Ran looks from the lever to the doorway.

"You don't suppose the door doesn't open while the bridge is connected?" Ran asks the group. "Maybe it has to be pulled back and that unlocks the door."

"Let's check this idea."

Meili raised up again to cross the bridge one more time. The only challenge for now should be to get around the new bridge decoration, but Meili hoped to squeeze around.

Should the lever be reached safely, she would pull it.

Mica pulls himself to his feet with Meili’s help and shakes his head to clear the cobwebs. “Thank you for the aid, Meili.”   He stares at the stone monstrosity in front of him “What happened to that?” He takes the poll of his hand axe and tries to chip off a piece of the stone, after looking at it curiously, he sticks it in his pouch as a trophy of sorts. 

He hobbles back to join the others at the gate, taking a moment to heal himself a little along the way.  He looks at the body of the fallen warlock and shrugs sheepishly at Nalomanterys “Yeah, I guess it was a trap after all.  Slippery little devil, he got what he deserved.” He listens at Meili and Ran’s conversation and agrees “Let’s see what happens.”

(heals 10 hp).

.

Meili is able to climb over the remains of the monster.  There is no path around it - its rocky corpse is gripping the edges of the bridge like a giant chameleon on a brach - but with the monster dead and nothing to rush her, it can be traversed slowly and safely.

The effort is for naught.  Pulling the lever raises and lowers the adamantine barrier at the other end of the hall, but has no effect on the vault door.

The only thing that stopped Meili from a frustrating kick to the lever was tiredness (she had to climb the monster on the way back as well and was not looking forward to it).

She left the adamantine gates raised and returned to the group. "Maybe you are right, Nalomanterys, and dwarves will know better how to open the door. We can rest and return with them here, to help if we did miss someone."

Mica groans as moving the lever has no noticeable effect.  He stares up at the door and the two locks. “Well it is made of the same stuff the gate was, so we aren’t breaking through it.  But I wonder if Ran can get through those locks”  He looks over at Meili “Sure, we could go back and get the dwarves, but aren’t you a little bit curious?”

Meili's quick smile acknowledged the joke but the smile died out as quickly as it appeared. And she again heavily sat on the floor by the door. "I am, of course. We fought all the way here, we might as well see what is behind that door. Any ideas on how to open it?"

"Well," says Nalomanterys, as he stands up to quite literally rise to the challenge, "there is a legendary tale of a long-forgotten Dwarven door. The door posed a riddle only when exposed to moonlight, and the answer was... Mellon." He annunciates the last Elvish word dramatically, as if expecting it might work here, on this completely unrelated metal Dwarven door.

He hangs his head dejectedly when nothing happens. "Well, let us at least see what these old Dwarves put up against intruders." He traces some patterns into a complex pattern in the floor as he ritually casts detect magic. As he draws, he casually remarks that these Newts probably never knew how to open this door in the first place, but just in case he asks his companions to search the two warlocks' bodies for the two keys to this door. Once the spell is cast, he'll walk the entire forge of Hrakhamar with the spell active to look for anything of interest - if it's Dwarven, he doesn't intend to steal it but will point it out to his companions. If he finds anything magical of Newt manufacture, he'll grab it as plunder and show his team.

Mica lets loose a sharp laugh at Nalomanterys password attempt. “An elvish password for a dwarven door? Would be strange indeed.” He looks back at the door “But the dwarves told us where to find the gauntlet, so there must be a way in.”  Mica searches the Warlock’s body again at Nalomanterys direction for anything resembling a key.

"Any welcome door mat with keys under it?" Maili even glanced at the floor in front of the doors but then shook her head with a smile. "Maybe under the chest then?"

She became serious and added "Can those two crystals be the keys? There are two of them, both are glowing..."

After trying everything else, Nalomanterys will try Meili's suggestion with the warlock's necklace and one of the fire quartzes from the chest. Unfortunately, he doesn't have the "Knock" spell in his spellbook, but he nonetheless tries to finagle the crystals into the keyholes to see if it will open the door.

While the others look around the door for a key, Ran looks at the lever that Meili pulled to no avail. That obviously doesn't work, but it does give him an idea.

"If the dwarves kept their best trinkets and whatnots in here, they probably didn't make it a breeze to find a way in," Ran says. "Maybe we're looking in the wrong place. Another lever could be hidden somewhere we can't get to from here."

Ran then goes back out onto the bridge, near the now stationary giant salamander and looks for another crossing or platform somewhere down the lava flow, including back the way they came into the caves in the first place.

Examining the door, there are two locks, one on top of the other, that seem made to be fit by keys.  The locks both show signs of damage.  While the door itself appears to be solid adamantine, the locks appear made of more mundane metals.  It looks has though someone - perhaps the newts - had been picking and then attempting to break the locks.  The fire-quartz, unfortunately, doesn't have any effect on the door or the locks.  Neither does the elvish word of power.

If someone wants to examine the locks more closely, they can do so with an Investigation check.  If someone has lockpicks and is proficient in them, they can attempt to pick the locks with a DEX + Proficiency modifier check (2 checks actually... first for top lock, second for bottom lock).

Ran, standing near the monster's corpse and looking about, you spot a ledge, on the same side of the magma but not connected to the area with the vault door.  There is no bridge or footpath to the other side, but you do see a heavy chain strung across the gap.  You would need to go back through the forge area to reach it and then have to shimmy across the chain, suspended over the roiling magma (Athletics check required).  From this vantage point, you can't see if there is anything on that ledge worth exploring.

Nalomanterys, ritual casting detect magic, you open your eyes and look upon the doors of the vault.  They glitter faintly, the adamantine ore used in their creation being slightly magical in nature.  The locks themselves are not magical and you detect no aura or sign of magical traps or wards upon the door.  

Walking through the forge, you find a few points of intellectual interest.  The bridge, most of the equipment in the forge itself, and the minecart bridges, are all magically preserved for resistance to heat and fire.  A lot of work went into building this place in such a way that it would stand up to the intense heat of the mountain.  You suspect that, were you to somehow visit this place in another hundred years, it would still be preserved in similar condition.  

The only magical item you come across is back at the body of the first firenewt warlock, the one you put to sleep and then was dispatched by your companions.  Next to its body is a small metal rod, radiating with evocation magic.  You also detect a strong connection to elemental fire.  From your recollection, the warlock was wielding this rod and conjured a flaming whip from it, just before your spell took hold of them.

Ran looks over at the chain and ledge, saving that for later if they can’t open the door.

He does go back to the door and takes a look at the locks the others have examined. Using the thieves tools he cobbled together, he takes a stab at both locks, hoping the newts haven’t damaged them too much.

Lock 1: 11  

Lock 2: 19  

"Need help?" Of course, thieves usually work alone but these were not ordinary locks and after so much fight in this unbearable heat an extra pair of hands could help. If only picking up fallen lockpicks.

(If allowed, help to Ran for advantage)

Nalomanterys grabs the scepter off the dead warlock and brings it back to the door. As he arrives, he waves the scepter in the air (as if to say, 'lookee what I found"). "At least we have something, if we cannot open the door. I found the magical rod the the first warlock was using as some sort of flame whip." With that he sits down again in the 'coolest' corner of the alcove and lets his allies fiddle with the locks. 

The wizard spends the time casting prestidigitation on his clothes to keep himself cool and clean, and mending on his robe which had a hole burnt through its backside. If the door takes more than 15 minutes or so, Nalomanterys will pull out a knife and begin to clean his soot-stained fingernails. He's ready to leave this stifling warren at any time and return to the Dwarves above.

Yes,  I will agree that help is acceptable.  These are quite large and complex locks, with some exterior damage, so there are ways the Meili might be able to assist Ran in this endeaver.

Also, lets resolve the lockpick before Nalomanterys gets back from looting the dead.

Ran's Second attempt with Meili's help:

Lock 1 9  

Lock 2 4  

(Wow)

(Very impressive!)