Peri:

Peri hears Kei's taunt, but he's too focused on the way ahead to respond. He has a feeling this corridor is leading to someplace good -- why else hide it behind the treasure room? He advances along the wall until he's close enough to mage hand open the door.

There's a short pause, and you hear Bayleaf grumble. "Yes, Sea Princes. The last time I dealt with them was when they burned down the abbey, looted it, and killed most of these nitwits." He adds a few dark expletives to this last sentence.

Meanwhile, Peri steps around the illusory floor and ventures down the northern hallway, getting close enough (30') to try to open the door with his arcane appendage. Pressing himself against the wall to Dodge any projectiles, he nudges it open.

...

Ballista attack (disadvantage from Dodge countered by built-in design advantage) vs Peri: 7 Hit: 18 piercing damage.

It misfires, the ballista having deteriorated with age.

Peri:

Peri, spooked by the close call, switches to the ceiling before peering around the next corner.

Peri carefully looks around the corner. It's ...a dead end.

But there are some small chests here.

Gerrard:

”You know, Master Kei, he doesn’t seem to be coming back.  Should we bypass this door carefully for now and try to catch up to him?  He might get himself in over his head without us,” suggests Gerrard, wanting to go forward by wary of triggering any hidden traps without Kei’s expert senses to suss them out first.

Peri:

Peri calls back down the tunnel. "There's some chests up here! Mind the traps though -- one in the corner and another trapdoor down this way." He takes cover around the corner and tries lifting the lids of the three trunks with the mage hand.

Kei 

"Never thought I'd be the sensible one of the group" he chuckles. "I think you're right m'Lord. Seems our halfling has golden fever, better go get him before he sets off some big trap." It's not 100% clear to Gerrard if Kei is concerned only about Peri or partly reacting to the talk of treasure chests. He makes his way towards the sound of Peri's voice avoiding the traps as directed.

Two of the chests open easily. They are full to the lid with hardtack – rations that appear decades, if not centuries, old. The third chest will not open.

Dwal just nods at Bayleaf's statement.
"Should have never left tha forge." Dwal thinks to himself.

Dwal strokes his beard for a moment then says to Boko. "We ain't gonna get a good look at anythin' comin' or if'n we got visitors, while sittin' here. I'm gonna have a look see."

With that Dwal will set out for the beach, or at least till he reaches a place he can have a proper look at the shoreline  where the skiff is moored.

Peri:

Peri is at first disappointed when he sees the hardtack, but he grins as he closes the lids before Kei gets there. "Make sure you check 'em for traps. This must be the big haul -- the REAL treasure. They're sure to be locked up tight."

From the top of the stairs, Dwal gets his bearings. The skiff is beached to the south. The booming sound is to the west. The mainland is to the north, and Saltmarsh is somewhere northeast. It's about a mile hike along a well-worn trail south (the way they came) to get to the place where he will even be able see the ocean (and perhaps the skiff.) To get to the eastern cliffs is about a half-mile hike through trail-less rocks and scrub and stunted brush.

Peri notes that the hardtack looks potentially edible, just not very appetizing. And very, very old and dry. 

Kei 

Peri's words are music to his ears. Finally they would uncover what these evil creatures were guarding with their un-life. He rushes up the hall, forgetting the unopened door completely, making sure to navigate the known traps. 

He rounds the corner and sees the unopened chests. "So, finally something your magic hand couldn't open." He saunters up to the chests and takes a knee. "Let's see what we have here". With a tremor of excitement to his hands he attempts to open the locked chests.

When two of the chests open to reveal nothing but hard tack he screams in horror. "You little...stupid....treasure my a....". He grabs a handful of the flat biscuits and throws them at Peri. If it wasn't for the third locked chest he may well have thrown a whole container at the skittish halfling. He attempts to open the final chest.

((If one can attempt a lock pick without thieves tools he will, otherwise he will bash at it as though it was Peri's undoubtedly laughing face))

DEX check 16 ?

Peri:

He cackles at Kei's biscuit-throwing tantrum. "Careful with those things -- they could be magic biscuits!" He laughs for a minute, but then starts to wonder: if these things have been down here for centuries, what's kept them from crumbling? Are the chests themselves special? He looks for an aura. Finding none, he waits for Kei to open the last chest -- probably gravy, but no reason standing close in case it explodes -- before examining the chests to see how they've kept their cargo whole for so long.

The third box will not open. It resists all attempts at picking, breaking, or otherwise. Peri detects an arcane signature to its construction, of indeterminate school. 

The first two chests are simply well-constructed and well-sealed. They've clearly kept their contents dry and stable for untold years. Nevertheless, the biscuits don't look very tasty.

Gerrard:

Sighing, Gerrard asks, "This isn't another one of THOSE boxes, is it?  I've already had enough with Aubrek's blue one."

Gerrard moves up to look closely at the third box...Does it bear a resemblance in any way to the special box Aubrek had them retrieve?  Any markings or characteristics which might give a clue to its origin?

History maybe?  22

Peri:

"Yes, powerful magics on this one! Wouldn't want the jam to spoil!" Another chuckle runs through him at the memory of Kei's face. It was pretty strong magic, though. Given nothing else has been magically sealed it must contain something valuable. "Wonder if Master Fiercehammer can crack it? We prob'ly need to get back to those two anyway. Out there chasin' birds and missin' out on all this." He gathers enough of the hardtack to refill one of the chests and carries it with him, already grinning at the thought of pulling the same prank on Dwal. Pranks were always better the crankier their victim was.

Gerrard:

Slipping the magical chest into his bag of holding, Gerrard says to Peri, “We have one more unexplored door to trigger…I mean, inspect.  Other than that I will trust you and Master Kei to divine the other secrets of this place or tell me that we have plumbed all it secrets.”

Gerrard examines the unopened box. It doesn't seem to have any immediate commonalities with Aubreck's box - his was metallic, blue, and seamless. This looks more like an old wooden captain's chest. It has no markings.

Peri:

Standing between the illusory floor and the untripped tripwire, still holding the chest full of biscuits, Peri tries the last door. He expects another rockfall, but wouldn't be surprised by a ballista either.