Tempe looks for anything, that might tell this creatures, story. Perception 21

Whoever... or whatever, emerged from the stone coffin took anything else that was entombed with him... it... leaving a totally empty resting place behind.

(This looks very ominous)

Zenodor looks for way out the thing/creature took. (More doors? A tunnel?)

There are no more doors or tunnels, the only way in or out would of been through the stone wall in the other room... unless it was erected after?... or maybe... teleportation?

Nothing else immediately jumps to mind.

Randall:

”Just in case,” says Randall, “let me see if the Dracolich’s phylactery is here.”

Randall casts Locate Object and tries to find the phylactery.

Zenodor: "Well, I guess we could try to return to the city ourselves. Perhaps the General, Mages or Priests have had some luck in their research while we were gone. And bringing them back the treasure we took will surely also help. I could cast Teleportation Circle to take us back to one of the corresponding circles in the major temples of the city.

But before we go, I think we should have another look at that 'fake' door in the treasury. It seems odd to just have a single such door - and not even as a decorative feature. Perhaps it was bricked up from the other side. Pepin, could we try to work our way through like we did with the wall?"

"Let us check the sarcophagus, it itself, may be what we've been looking for." He ritually casts, detect magic, then checks the sarcophagus out, then checks the fake door. And if he can the rest of  the area.

((we haven't checked out the temple yet, right? Or at least very little?)) 

True.

This place was discovered almost by accident and diverged from the original temple's location. It was a separate structure that has nothing to do with the temple really.

Quote from Secretfool >>

((we haven't checked out the temple yet, right? Or at least very little?)) 

 (Fair point. The place we came from only had the two paths, no? The one with the dead-space-orb, and this one we went through? Or do you mean further back?)

Randall:

(Once Randall has finished his spell, he will help look for secret or hidden doors.  Passive perception:  20.)

Quote from Touschka_ >>

Quote from Secretfool >>

((we haven't checked out the temple yet, right? Or at least very little?)) 

 (Fair point. The place we came from only had the two paths, no? The one with the dead-space-orb, and this one we went through? Or do you mean further back?)

 I meant further back, where we discovered a hole in the temple wall I believe. The temple we started in was that where the elves were, and where their guide was lost. So when we finish here I think we should head back the way we came to further investigate that temple.

Randall doesn't find the phylactery here. And the only door that stands out is the false door. (not as being a secret door or anything, just that... what's the purpose of it?)

The elves that tasked you with ensuring it was safe to explore their long lost temple have no clue that this other structure is buried underneath and off to the side of their temple. None of them have entered yet, they await your return.

"I agree lets do it."

Randall:

”I see nothing of further use here.  Let us return to the temple proper and keep exploring,” agrees Randall.

As they wander back towards the main part of the temple, Zenodor wonders aloud: "I am a little concerned that this second hidden underground vault may endanger the elves. What if its owner comes back at some point? At the very least, we should close the wall again [shape stone perhaps, if someone has it?]. Or would there perhaps be a way to collapse the tunnel? That should keep the temple safe from future intruders. Pepin, this seems your area of expertise. Any ideas?" 

((If it works, Pepin can cast stone shape to close the wall back off))

You can use stone shape to rework the wall so it seals off the area again.

"Yeah I can do that, sure thing." Pepin answers Z before casting stone shape and getting to work on it. "Now let's get back to what we were actually here for"

Quote from Secretfool >>

"Yeah I can do that, sure thing." Pepin answers Z before casting stone shape and getting to work on it. "Now let's get back to what we were actually here for"

 (Love it. So, just to recap: we broke through the back door into a secret vault, stole a whole demiplane's worth of treasure, and now sealed the wall back up making it look like no one was ever there. Maybe the next campaign should go into heists and robberies)