Krom after examining the deceased members of the Black Swords, stands up and nodding to Rhogar climbs on the boat. 
"I gladly leave the oars to you my friend" says the dwarf with a big smile "You know well that I am not very fond of boats." Krom scratches his beard for a moment before continuing "What do you think happened there?" he points at the room with the bodies "Traitors maybe? Tomorrow I could prepare an hymn to ask them a few questions, but they may not know much..."

Quote from MaxHam >>

Krom after examining the deceased members of the Black Swords, stands up and nodding to Rhogar climbs on the boat. 
"I gladly leave the oars to you my friend" says the dwarf with a big smile "You know well that I am not very fond of boats." Krom scratches his beard for a moment before continuing "What do you think happened there?" he points at the room with the bodies "Traitors maybe? Tomorrow I could prepare an hymn to ask them a few questions, but they may not know much..."

(Sounds good to me. @DM what time of the day is now?)

Kazri does not find any valuable information in the hallway, so she just keep guard.

Perception: 12 (In case it's needed)

Chill felt the tap on his shoulder and then the magical electricity flow through him.  He shuddered for a moment and then exclaimed "Is this what it feel like every time you use magic!  Its amazing!"

Feeling the bouyancy he floats up into the air and tries it out trying to get the feel for it.  He then starts across the water towards the closest entry in the walls.  "No use wasting it it.  Wow thanks Rhogar."

Chill has the biggest shit-eating grin he could possibly have as he floats over the water to close opening on the north side and looks inside.  If it looks safe he lands on the ground and pokes about.

(Kazri, I think maybe you missed that Rhogar gave you the ability to fly. )

As Chill heads to the first opening he looks inside and sees it is safe to land.   Looking about he sees the room is empty except for a rat that chews through the corner of a sack of grain lying on the floor.

Chill checks the room and when he finds nothing he reports that to the others as they approach. 

"Nothing here.   Let's continue to the other doorway."

He then flies over the water to the opening on the other side and looks in from the edge.

Chill lands at the next passage which is on the south side.  Looking inside he sees that frost covers the floor of this dark, fifteen-foot-square room. To your left and right are narrow tunnels, and across from the entrance stands an eight-foot-tall pillar of ice with a horned, pale-skinned, humanoid figure trapped inside it. The pillar is wrapped in black chains, and the wall behind it is covered with brown fungus.

As you wait for the others to catch up you can safely step in further.  Looking quickly into the other rooms to west you see red rug, a narrow bed, and a freestanding mirror in a wooden frame, none of which are remarkable.  There is also a small desk.  On the eastern side this unlit room is empty except for an iron lever that protrudes from an iron plate embedded in the north wall.

Now that you are closer to the far end of the cistern you can also see that the eastern end of the cistern is a 10-foot-square, 2-foot-thick, half-submerged slab of blue marble

(Sorry about that.)

Rhogar touches Kazri on her shoulder and says, “Here it goes. You can fly now.” She has no doubt of the Dragonborn’s powers, but the Paladin is still slightly skeptical. “Thank you Mr. Nimbatuul.” She takes a couple of steps towards the water then she starts to levitate. A rare smile shows in her face. “I shall inspect the eastern end of the hallway.”

Rhogar at least had the decency to offer Krom an apologetic smile, having forgotten the dwarf's personal quirk, and would endeavor to make the trip as smoon as one as possible. But between needing to navigate around the ice floes and the narrow confines itself, he could only row them along so quickly without ocontradicting this desire, so held his tongue on even a joking complaint at the fliers. "Find something interesting this go around?" Rhogar asks when he and Krom finally up up to the second passage; but otherwise, he stays in the boat for the time being.

Krom, being full aware that falling from the boat in full dwarven plate would bear an unpleasant consequences, stays still as much as he can. The dwarf from time to time nods at the dragonborn in appreciation of his smooth rowing.
As the boat finally stops at the second passage, if Krom finds himself in a position where he can clearly see the horned humanoid trapped within the chained pillar, he will attempt to gather more information about him (Religion 11). If he is unable to see clearly inside the passage, Krom waits patiently for Chill's report.

Chill swiftly moves through the adjoining rooms and finds no one.  It appears safe and reports what he sees to the others.

The desk is the most curious item for him and let's the others ponder the frozen being.

He checks the desk for traps and then will try and open it, picking any locks as needed. 

Perception 16

Thieves tools 33

Kazri started to fly out over the water but it didn't take long when she became disoriented.   Darkness surrounded her and she couldn't see. Back to the west the faint glow of the torches remained.   But she knew if she kept going she would run into a wall or something else. She couldn't see in the dark. 

Where were the doorways? She couldn't find them.  If she didn't fix this soon the magic would run out and she would fall into the frigid water below. 

Krom cannot distinguish anything specific about the figure frozen in the pillar from his place within the boat.

Chill makes his report to Krom and Rhogar who are in the boat at the edge by the southern passageway. 

Chill then heads into the one room.   It looks like a bedroom and someone has clearly been staying here and very recently.   The desk is of most interest and he checks it out.   His inspection reveals that it is both locked and trapped.   It seems anyone who tries to open it without the key would get a very nasty poke of something.   The needle is sharp and has some black poison on it.

Chill expertly disarms the trap and releases the lock. He is then able open the drawer to the desk. 

Within the desk Chill finds 2 items of interest.  First is ring and the second is a belt.

The belt has the face of a dwarf on it. 

The ring is silver with blue gems that sparkle like water. 

Kazri despairs for a moment, but she takes a deep breath to calm herself down. She locates the faint glow of the torches then she moves backwards, she believes that eventually she will hit a wall.

Intelligence: 16 (If needed)

 So used to seeing clearly even in the gloomiest of places (barring the one in the vision), it took Rhogar a little time before it dons on him a member had gone missing. Worried, he immediately began looking about for Kazri, fearful in the dead having arisen and snatched into her the chill depths beneath them! "Ah! Lady Kazri! Over here!" He called to her. "Oh! Right! Human, uh.. a moment!" The dragonborn furious fished about his person before eventually producing a silver piece. A gentle few words followed by a soft breath over the coin then sees it sparking with electricity and emanating a bright light that he holds up for Kazri's sake. "There we are! Much better, yes? Heheh. But please, this way."

"Yes... Yes!! Much better. Thank you Mr. Nimbatuul!" Being able to see better, Kazri turn towards the west looking for a place to land.

"Sorry lass, I should have placed my light on your shield and not mine." says apologetically Krom to the paladin. 
The dwarf listens carefully to Chill's report "The tiefling wizard that flew away probably made that room hers while she stayed in the castle. Beside those two masterly crafted items, have you found any notes, scrolls or any other parchments? She was up to something for sure. Maybe she was trying to free that being frozen inside that pillar." asks to Chill while pointing at the being inside the pillar.
"I can not discern anything useful from here, it's better if I get closer." Krom hops off the boat and walks towards the pillar in order to have a better look at the creature inside.
"Rhogar, what do you make of this? Your arcane knowledge may gain us better information than mine."

Rhogar offers the glowing coin in passing to Kazri once she grew close enough, then just about settled back into the boat before the call goes out, grabbing his attention. "Mn. I was taught many an esoteric things by brother Vixix, so I can give it a try. But, I can make no promises for something native to this particular region, as we are a fair bit north of places even Brother Vixix once roamed before settling in the hills near my home time." Rhogar freely confesses, only pausing briefly mid-way to focus on climbing out of the boat.

Once inside and able to see the creature even the Dragonborn appeared taken aback for a moment, but quickly would regain his composure and start studying the creature's form with a little whispered aid from Vixix.

-Arcana: 15.

Chill set the items aside for a moment and searched the rest of the desk.   He then grabbed the two items and showed them to the others.

"Some sort of lever in the other room"

He then points at the frozen creature. 

"So what, or who, is that?"

Kazri is about to turn back to where the landing was but Rhogar creates a source of light and she is able to catch up.  She lands in doorway and is rejoined with the others.

Rhogar and Krom disembark from the boat and move forward to inspect the frozen creature. Upon closer inspection they can see that the figure in the pillar is a wooden mannequin painted and dressed to resemble what looks to be an archdevil.  You figure it likely is Levistus and can guess that the cultists use this frozen, chain-wrapped effigy as an altar.

Rhogar and Krom please make a DC 12 Constitution saving throw, taking 28 cold damage on a failed save, or half as much damage on a successful one. 

No bonus from Kazri as she is not close enough.

-Rhogar's Con's Save(DC 12): 24.
(Damaged halve again thanks to book.)

"Wait... is that... Levistus?" Is about as as Rhogar gets before what happens... happened.

"Levistus you say? You are right, Rhogar, it is indeed an image of the archdevil." says Krom as he approaches the makeshift altar.

Krom's Con save (DC 12) 21 (Damaged halved thanks to the ring of warmth)