How To Deal With a Backwards Enveloping Pit

[Etarran]

In a recent game, my party and I stumbled across a very interesting magic item - it's a trapdoor that, when opened, cannot be moved by any means and leads to a large stone room (40 feet wide by 40 feet long by ten feet tall). The catch, however, is that it can only be opened from the outside - if the door is shut, it cannot be opened again from the inside, trapping whatever has gone through it.

The question is, how do we deal with this? Obviously, this makes an excellent storage space or prison, but part of the fun of extradimensional spaces is that the party can use them as a mobile base and be safe while inside them. I thought I'd bring this puzzle here and see if the collective brains of min/max could dream up a creative way to make use of this neat piece of gear.

The party, in case it's relevant:

Wizard 5 (conjurer, abrupt jaunt, focusing on battlefield control)
Sorcerer 6 (blaster, using born of three thunders and lightning substitution)
Bard 5 (Support/ off melee)
Feral monk 1 / barbarian 1 / psychic warrior 2 (my character, focusing on grappling and natural attacks)

We have a fair bit over standard wbl, but store access to only common magic items in the smallish town we're in.

Interested to hear your ideas.

[CantripN]

If trapped inside, you might be able to Dispel it long enough to leave. Or you can leave one party member outside to open it.

[X-Codes]

Unseen Servant.

[Etarran]

If trapped inside, you might be able to Dispel it long enough to leave. Or you can leave one party member outside to open it.

I like that idea, but we are not sure if it is an extradimensional effect or a teleportation effect. Finding out the hard way could be a problem.

[CantripN]

If trapped inside, you might be able to Dispel it long enough to leave. Or you can leave one party member outside to open it.

I like that idea, but we are not sure if it is an extradimensional effect or a teleportation effect. Finding out the hard way could be a problem.

If it's a [Teleport] effect, you're implying it's a Mobile Portal. Those things are... expensive. And a lot easier to get out of, eventually, as you'd just use Teleport to get out. If it's Extra-planar, all the better! Think of the uses!

It could perform rather well as a base of operations for you if it's a teleportation device, really. I could even see some use for Divert Portal or one of the many ways to mess with Portals, if it's one. It could serve as a Stargate of sorts, except it's a mobile one.

But I really doubt it is. More than likely it is simply an extra-dimensional space.

[Prime32]

Can you escape in gaseous form?

Does the portal cease to exist while the door is shut or is it just blocked?

[Etarran]

The door ceases to exist when shut, so probably the gaseous form escape wouldn't work. We could try breaking through the stone walls of the chamber, but without knowing what is on the other side, I am loathe to do that - not knowing the mechanism is crippling, because I don't want one of our experiments to suddenly make it stop functioning. We know it's a conjuration effect, but that's it; Identify gave us no answers. (However, when the door is closed, the area where it should appear does not give off any magical aura, which is why I believe it might be a [Teleport] effect). I believe the item may be Plot Central, which would explain the enormously out of scale value.

Of course, waiting a couple levels until we have access to Teleport would be the easiest way to determine that, but we would like to begin using this as a safe base of operations as soon as possible, since obviously that would be a powerful effect.

The solutions of leaving a party member outside, or just leaving the door standing open, strike me as unsatisfying. That's what we'll have to end up doing if nothing else presents itself, but the prospect of having the door closed while we are sleeping (say, if the party member was stealthily attacked or dominated) is not a pleasant one. Something like leaving the open door against a surface and concealing it with a silent image is a little better, but if something so much as accidentally knocks against it and closes it we are fucked in the portable hole, as it were.

So I guess more specifically what I am asking is: Is there a safe way to leave the door open with all of us inside it, or is there a surefire way within our means to tell what kind of effect this is so we can figure out some way of leaving the door closed and still being able to leave easily (and if so how do we protect the entrance properly, since it can be opened again from the outside).

Thanks for the help so far!

[CantripN]

You could try using spells that work through the planes, as compared to spells that don't. I'm not sure this would work, but you can try. Failing that, check if you can summon things in there, and see if you can use things such as Telepathy from there (it doesn't work cross-plane).

Simply seeing if you can use a Benign Transposition / Abrupt Jaunt to cross sides could do, I suppose. It doesn't work through the planes.

Try Analyze Portal (SpC) to see what it is. It's a 3rd level spell, well within your casting ability.

[dna1]

So I guess more specifically what I am asking is: Is there a safe way to leave the door open with all of us inside it, or is there a surefire way within our means to tell what kind of effect this is so we can figure out some way of leaving the door closed and still being able to leave easily (and if so how do we protect the entrance properly, since it can be opened again from the outside).

Thanks for the help so far!

you could leave the door open and cast like a hold portal spell on it right? that atleast would make it so you dont have to worry about some ass hole shutting the door while your in there. then just cast some alarm spells around the entrance?

[PhaedrusXY]

That doesn't sound backwards to me... maybe sideways. The Enveloping Pit is supposed to be a trap. So the original probably shouldn't be open-able from the inside, either.

If you're worried about it, I'd just suggest not sleeping in it. Use a normal Rope Trick for that, and just use this thing as a storage area/prison. Later, you might consider using it to ferry party members around once one of you get Teleport, but that's probably at least as dangerous as sleeping in it.

[Foxwander]

You could use my idea from the other enveloping pit thread - use a shield secured with an immovable rod.  Heck, forget the shield.  Get a custom-made cover that fits around both the entrance hole and the open trapdoor AND designed to make a flat seal with the ground.  Hinge it down the middle length-wise so it can fold up to store inside your mobile base and put brackets on the bottom to hold your immovable rod.  Instant secure cover for your "open" trap door!  

PS- don't forget your air bottle and wind pipe!