Standing in front of the double doors, Kazri lightly pushes one of them, just to check if it is locked.

Chill looks around but his keen sight shows no weaknesses or easy points of entry.  The only ways in would be climbing.  Either through the eyes that appear to be open or to the roof.  The roof, where presumably, the roc would likely be if it were present.  The climb would not be easy up the ice slick sides of the fortress but perhaps in time could be managed. It would be 40 feet to the level with the open eye sockets and 80 feet to the roof.

Meanwhile, Kazri gives the door a push. The door is 25-feet-high, and 8-feet-wide and it moves slightly and she thinks, given enough effort and some help, she could push it open.

"What do you say Chill? Have you found a way up or other points of entry?" asks Krom as Kazri attempts to push the door. "If there are no other way, I guess that we will have to open the doors hoping to not get the attentions of the giants."

The dwarf prepares himself to help opening the door while also readying an hymn of Guidance.

"Do you want to climb? The walls are slick with ice.  I could climb up and anchor a rope and we could all climb up.   But we don't even know where the codical is.   We may be passing it by and missing it. It may be easier to start at the bottom and go floor by floor."

Chill answer Krom

"You raise a good point, Chill. Not to mention, if that Roc is here and not on some other high point on this island, which I rather doubt, it is not unlikely up top. Which would make this tricky, to say the least." Rhogar comments while limbering up and readying to provide his own assistance, even if only as some token effort. "I'd send Gorrah at least for a peek, but there's folly even in that. So, let's hope for the best, get this blasted door open, eh?"

Rekuberk will make his way over to help with the door as well, looking over the fortress before he gets to do the door and presses himself against it to push forward.

"You have a point Chill, let's open those doors." The dwarf puts all his weight and strength as he help the group pushing the doors open. 

"I trust that the Professor will be able to identify the Codicil if we walk near it. I can not locate it as I did with the Orb."

“Very well then, be ready gentlemen.” With that said, Kazri and her companions carefully push the door, trying her best not to make too much noise opening it.

Strength (Athletics) check, with advantage and guidance to whoever is pushing

Kazri Athletics: 20 + 2 Guidance

Rekuberk cracks his neck and moves to push against the door as well.

Athletics: 23

Kazri and Rekuburk both put a shoulder against the heavy door.  With their combined strengths they push the doors open.  The entry is 20 feet wide and runs to the west, the ceilings are 30 feet high.  All surfaces (floors, ceilings, walls, and so forth) are made of smooth, opaque, chiseled ice with a bluish tinge. A 2-foot-deep blanket of cold mist creeps across the floors. The rooms are not illuminated in any way and you will need some sort of light for those who cannot see in the dark.

Ahead of you to the west, those with darkvision can see a set of open doors that lead to a long, rectangular room (G2) that  is strewn with pieces of rotting wood and rusted metal—the remnants of giant weapons and weapon racks. A rusted-out helmet sized for a giant lies near the back wall.

To the north another hallway runs into the darkness.  A couple sets of doors on the right and openings on the left and end of the corridor.

"This fortress has seen better days, I thought that giants still lived within." says Krom as the group enters. Noticing that there are no sources of light inside, the dwarf touches Kazri's shield murmuring a hymn of evocation (Light). 
The dwarf looking around says "I do not think that we will find the Codicil in this floor, but nevertheless I think that we should explore all rooms before proceeding downstairs or upstairs." Krom points at the open doors at the west "Starting from that room." He pauses for a moment before adding "All things considered, the giants, or at least some of them, may be still within this fortress as undead guardians. We know that the Frostmaiden uses such abominations as her servants."

Slipping through the doors as Kazri and Rekuburk push them open Chill enters the hallway.  Seeing the first room empty he moves up the hallway to glance into the rooms with open doorways to check for anyone.  He'll leave the doors for the others.  If they are like the first he didn't have the strength to open them.

Kazri readies her shield and sword, and follows Chill closely.

(I guess she will be judicious with the Divine Sense since this seems to be a pretty large place.)

Chill moves forward and looks into the open rooms.

(G5) Through the door way to the left you see shattered chunks of ice, the remains of a door, lie strewn on the floor around the opening. In the middle of this immense hall stands a thirty-foot-long, ten-foot-wide, ten-foot-high dining table carved from ice and surrounded by a dozen blocks of ice that once served as chairs. Wooden braces against the west wall hold a pair of fourteen-foot-long bugles made from hollowed-out mammoth tusks. An ascending staircase of ice in the southwest corner has mist rolling down it.

Ahead of you (G6) more shattered chunks of ice lie on the floor around the opening where the door once stood.  Six slender, gargoyle-like creatures made of ice squat on ledges twenty feet above the ground that protrude from the wall of this semicircular chamber. Near the back wall, the mist that blankets the floor flows down a staircase made of polished ice.

The other doors on the right remain closed and require a DC 20 Str (Athletics) check to open.  

Kazri waits for everyone to be ready, and she will try to open the first door on the right (G3).

Kazri Athletics: 18

(If Master Krom provides some Guidance: 1)

 "All very fair points, Master Krom. Here's hoping if there are any, they are of the physical kind over the spiritual. For I do not relish facing some giant version of those balls of light we saw back in that other grave." Rhogar comments idly while following after the others. Apart from that, when Chill returns of news of his findings closer to the stairs, Rhogar would wince, look away muttering something, and frankly becoming a bit caught up searching his mind for any recollection of such a creatures.

Recall Details on "Ice Gargoyle": 18.

If Chill however keeps quiet, then Rhogar utters a small prepatory cantrip as Kazri(with help from others?) saw to the opening of a door.

As Chill explores the rooms within the open doorways, Krom says "I'll check the giants' armoury in the meanwhile." The dwarf, shield and war hammer at the ready, walks to his left inside checking the armoury (G2)  . (Perception 5)

After finishing to check the room, Krom, seeing Kazri attempting to open the first door on the right, says "Let me help lass, that door looks very heavy and probably the hinges are frozen." The dwarf, chanting an hymn of guidance on Kazri, puts all his weight and strength as he help the paladin.

Kron checks the first room they passed but finds nothing of value or worth salvaging.  He moves to help Kazri.

Even with Krom giving guidance and helping try and push the door open, Kazri can't only get it to move slightly.  She is sure it could be opened, it certainly didn't seem locked.  But she and Krom just couldn't get good grip on the floor with their boots.

Perhaps Rekuburk with the help of Rhogar would have better luck?

Chill likely tells the others what he has seen but without having seen the carvings himself he can't think of anything specific about them.  Probably just ice carved gargoyles.