Choir feels like she can figure out some of the tools but to really understand it she would need a lot of practice. The good thing, though, she has someone right here to tech her (in time) - Fran caring her own set of lock-picks for a reason. 

Fran would smile watching Choir check out her new set of tools. The artificer would approach her with her own set and show her each tool, telling her what each one is called and when she’d use them. It was a mini crash course to pass the time until all were ready. 

Choir's eyes widen in amazement at Fran's expertise! How lucky she is to have a teacher with her.

After adequate time to rest Adray says, "Alright, breaks over.  Let's get on with business."  He then heads over to what appears to be steps leading down from the alter room.  He has his spear in hand and waits for everyone else to fall in line to support.  Hes got his spear in a hand and thieves lantern in the other.  When alls ready he'll head down.

Perception 18 + 1

”Guess we’re as rested as we’re going to be! I managed to gather some magical power as well!” 

She looks around to see if anyone is willing to carry her but she wont ask for it. If no one does, she will swim, which she does not look forward to.. 

(Marching order and - specifically - Choir with her light shield position. Also, how do you use the lamp? As a lantern illuminating everything 40ft around, or more like a flashlight?)

Steps to lead down to yet another flooded corridor (someone really aught to help little mage, caring now 3 more precious spell-books). To the right (and very close) - stairs leading up again, to the left - flooded corridor probably turning back to the room you just left. At least there is a turn and in that direction.

(Choir would definitely renew the light spell before proceeding. If the two fighters lead, she will go third...if one of them is starting to feel ragged around the edges, she can move up in marching order.)

Fran will scoop Polly up newlywed style to carry her through the water. She'd take rear in the marching order.

Adray has the lantern in flashlight mode for now.  He'll relay the information to the others regarding the intersection.  "If the hall to the left leads back up to the area we were still in.  It might make sense to clear that out so less risk of having someone sneak behind.  Plus aren't the worse things in the deepest rooms?"

"You've got my vote."

Ordrag will follow directly behind Adray and in front of Choir. He notices that although Adray can confidently see the illuminated area in front, his peripheral vision consequently suffers, so Ordrag sweeps his darkvision side to side from the second rank, weapons at the ready to avoid being surprised by lurkers in the dark.

OOC: Let's do some math: Spell "Light" - Until the spell ends, the object sheds bright light in a 20-foot radius and dim light for an additional 20 feet.  Equals, 40ft radius of light.

                                              Lamp: A lamp casts bright light in a 15-foot radius and dim light for an additional 30 feet. Equals, 45ft radius of light.

One square is 5 ft, corridor wide is 1 square (5ft). If each player takes on square, Adray is 10ft ahead of Choir.

Technically, lamp would give 5 more ft of bright light ahead and 10 more of dim light, but still sounds like a waste to me.And at any rate, "hidden" approach would not work with all that illumination.

Btw, "thief" lamp - is sort of a homebrew, but this is a kind of thing that existed for centuries and must be invented in Faerun as well. It's less about focusing light, but more about keeping whoever holds the lamp in the darkness, leaving only lamp visible. Of course, when someone is illuminated from behind (like Adray now), the hidden factor is voided.

The group went up the stares and practically immediately bamped into another door. Being carefully opened with expectation of anything on the other side, the door revealed just another corridor, turning left but with the opening to the right. From there you can hear a distant chanting (?) or something like that. It sounds unpleasant, but what does sound good in such place? Though, come to think of it, the whole place feels more like a working lightly populated HQ - some rooms are empty, but inhabitants of the others are simply minding their everyday business, as nasty as this business is. Most likely, someone in the room ahead is working on his own project oblivious to things outside.

Map:

”Maybe I should send in Owis to see whats what? That chanting sound quite ominous.” 

Polly glide into Owis mind and then they run in to the corridor where the sound come from. 

Perception Owis: 
17

Actually, Owis was in a severe need of Hiding check, because first thing he saw in the room (after yet another corridor, though short and dry for a change) was a swarm of tiny skeletons - rats skeletons, fortunately grouping around toll frighteningly thin figure in a - you guessed it! - black robe. The room itself is partially collapsed with three wooden beams bracing its ceiling. Situated between the beams is a scorched wooden table with a human cadaver resting atop it. The figure (that looks like a woman, though her face largely hidden under a cowl) is clearly weaving some magic that has something to do with the dead body on the table.

When Polly/Owis sees the dead rats and the woman they immediately hide where they can observe the goings on. Polly will relay everything she sees to the group, but she can not hear them if they try to ask her something. 

Stealth:   20

Rats are preoccupied but there is so much amusement in necromancy - there is no doubts the necromancy is involved here - that an animal, even dead one, can take. Polly is unfamiliar with the spell used here but Owis can see the the dead body on the table jolted and the dead hand formed a fist.

"Damn, is this how they make them undead?  I think they are making her undead.  Let's not wait they finishes," whispers Adray to the group.  He continues, "If Nibs and I attack her, can ya all hit those rats?  Melt them with acid or somethin?"

Choir clutches her warhammer and shield, ready for battle.  She supposes her last spell is too precious to wast on Thunderwaving a room full of rats, but if it comes down to that...

Fran would nod, “You bet.” The artificer will tap her wrist on the wall, tink, to ready her acid splash. 

Ordrag replies: They don't look like no cleric of Torm, eh! Let's drop 'em.

OOC: By the way, I'm still learning 5e, and decided to read up on 'surprise'. I didn't realise they don't really have 'surprise rounds' like in older editions. This is from the PHB:

So before initiative is rolled, and in fact before positions are even determined, EVERYONE that is trying to be stealthy must pass a Stealth check against the passive Perception of each of the enemies. Each enemy that doesn't detect ANY attacker gets the 'surprised' condition. Then we all roll initiative and go from there. The difficulty is that in a party of 5 or 6 there is a good chance that at least one player will get a crappy Stealth roll. There's not really even an option of 'just send in the stealthy ones first'. 

So perhaps with us sneaking around this dungeon, we should ALL be rolling Stealth checks every time we come across a potential encounter. Most of the denizens are probably not being stealthy as well, but the DM can decide if they are, and roll Stealth checks for them against each of our pPerc to see if WE are surprised.

Thoughts?