Joetaro turns to the others. "No evil beyond this door that I can sense."

As Rhayna notices the difference in this new place. "Ohhh... This is interesting. This architecture doesn't look like it is from around here my friends." She also believes that it is probably not demonic in nature, for it seems that Sarith is not having one of his "amnestic" episodes. She does not confide that fact to her companions yet, for she would like to gather more evidence, before revealing her findings about Sarith. She goes to study the stones, and after fixing her glasses, takes a closer look at the door. She opens her Journal, and starts to "catalog" it. As she does that, she tries to determine if there are any markings, and if so, if she is able to decipher them. (History: 25)

(I would like to add that Rhayna is not touching anything, just observing and cataloging.) Rhayna crouches down next to Stool. "Hey Stool, are you able to communicate with the voice?"

Kaylyn follows behind the others still wary and leaves the door for the others. 

Settling himself, Kastix turns to everyone with him, "Beside more like Stool, what else should we expect?"

"I do not think the creature inside is like Stool," very seriously answered Sekkar, "that one feels differently, like that power in the lake. Lighter, but still powerful." Lizardman checked the door too - mostly for the right point to apply brute force - and tried to push open it. Pure Strength check?  23  (That was Athletic check, meaning + 2)

Rhayna: Stool did not hear the voice, but then it can only communicate in a limited area with those under the influence of its spores. 

Sekkar sees that the door pivots on a central axis, and with a grunt and a push the lizardman gets it to turn, forming narrow passages on either side which lead into a 30-foot by 30-foot room.

A stone diorama stands to the right of the entrance, depicting a half-elf noble in her prime, surrounded by attendants, slaves, and other trappings of wealth and power. A vista of fantastic floating cities covers the wall to the left of the entrance. Across from the entrance, stone torch scones flank a dusty staircase descending 20 feet to a landing. The torch sconces are empty, but the interior is illuminated by the faerzress that continues to pervade the area. Set into the back wall of the landing is a calendar stone, and beyond the landing, the staircase resumes its descent.

(I'll extend the History check to all aspects of this location, and describe Rhayna's observations along with the more mundane descriptions)
To an archaeology buff like Rhayna, this place is like all her birthdays have come at once. Most of the group will have heard of Netheril, the ancient empire of mages that ruled Faerun from magic flying cities, and their forgotten lore is legendary and full of powerful magic. It could also be assumed that Rhayna would know of the major nobles of the Netherese history, and she recognises in the picture the figure of Brysis Khaem, a half-elf sorcerer of some power and reputation. This structure appears to be a tomb, but how it got down here in the Underdark is unclear. Most of what you've seen in this part of the Underdark is like granite, but the rock in this island is like marble, and highly polished within the tomb.

Sekkar was from the part of the group that never heard word "Netheril", and, frankly, did not care either. His curiosity concerned only living (moving) beings and the danger those beings could present. He touched the wall studying the unusual stone. "Interesting rock," declared Sekkar, carefully moving deeper inside (searching for traps, as he go, and first touching steps and walls with the sword, only then stepping himself). (Perception 15 )

Joetaro is going to hang near the back of the group and continue to observe the stone.

Kaylyn looked up at the image of the half elven woman.  She knew vaguely of the Netherese but no more than the legends.

She casts Detect Magic to get a feeling of the room.

"We have a voice asking to be freed and we're at a grave. Try not to get possessed," Kastix whispers when he makes his way into the chambers, careful not to touch anything more then needed. 

Sekkar senses nothing unusual about the room, but judging from the echoes returning from the stairwell, he would say it descends about 100 feet. As Rhayna enthusiastically scribbles in her journal, Kastix and Joetaro cautiously stay on alert. Kaylyn casts her spell, but peering through the faerzress she can see no hint of any of the familiar glow indicating the presence of magic. Suddenly Sarith drops his shortsword, crouches over and vomits onto the floor, narrowly missing Zeno's feet. Through the telepathy of the spores he apologises, saying he doesn't know what came over him, but that he feels sick to the stomach. After another up-chuck the drow staggers to his feet and heads to the door, saying it might be better if he guards the entrance.

(Forgot to mention, Hemeth stayed behind with the boat. There was probably some mistrust associated with this, but Hemeth reassures everyone that he has nothing to gain by marooning them on the island and venturing out alone).

"Nothing magical in here." Kaylyn quietly says as she moves to follow Rhayna.  Emboldened now to help, and watch out for, her friend she follows Rhayna down the stairs.

After Rhayna is done documenting the Diorama, she goes down the stairs and studies the calendar stone.

Then Sekkar still carefully heading down.

Joetaro is going to carefully walk down the stairs as well.

The stairs descend back and forth to three more landings of bare stone before opening into another room. Against the left wall stands a shrine, which Rhayna quickly observes is dedicated to Mystryl, the Netherese manifestation of the goddess of magic. Flanking the shrine are two friezes on the walls, one depicting the goddess Shar and the other Selune. Shreds of dusty tapestries lie scattered on the floor, victims of the ravages of time. Two closed doors, similar to that at the entrance, lead out of the room.

Sekkar smelled and tasted the air. So far he did not see anything dangerous (or interesting) down here, but you never know with the old abandoned ruins. Though, this place did not look like a ruin. He looked around at the friezes and asked Rhayna, that eventually made it to this room too: "Does it tell you what we should find behind the doors? I do not sense danger but still do not like it much here."

Quote from BlueBayou >>

Sekkar smelled and tasted the air. So far he did not see anything dangerous (or interesting) down here, but you never know with the old abandoned ruins. Though, this place did not look like a ruin. He looked around at the friezes and asked Rhayna, that eventually made it to this room too: "Does it tell you what we should find behind the doors? I do not sense danger but still do not like it much here."

(Does Rhayna knows what lies ahead?)

Zeno’s danger send had been raised at the mention of the word tomb, followed by that other feeling, the one that usually got him in trouble. Tombs belonging to the wealthy were sure to be full of shiny, expensive things...

He checks the two doors in the shrine room for traps.  14