A very interesting idea...

[Lupy]

I've been thinking about making a campaign world set underground, but with ceilings hundreds of feet high and painted sky colors. The players will notice it's always either night (in which case the overhead lights look like stars and moons) or day (in which case there is one bright "sun"), depending on where they are, but I don't think they'll realize they are underground.

I'm thinking that each cavern will be separated from the next by a large underground lake, which will give the impression of islands, some larger than others. Eventually (Level 14ish), the PCs will find the entrance to the surface world... Which will just be a beach on the edge of the astral sea.

What do you think?

[Eloel]

For the session when they'll find the exit from the caves, wear a helmet. There WILL be books flying around.

[Zergrusheddie]

Nifty idea. Here is a strange suggestion:

The come upon a room where people are found in a trance-like state. Among these group of people, the see themselves, though they are struggling against the chains that bind them. If they break the chains, they leave the Underground.

The Allegory of the Cave FTW!

[Lupy]

For the session when they'll find the exit from the caves, wear a helmet. There WILL be books flying around.

Huh? Why would they be angry?

[Starscream]

I like this idea. How will you handle weather and things? That might be the best giveaway for an observant player.

And are the characters people who have been underground their whole lives? If so, they probably won't notice anything odd with the terrain.

[Nightson]

Don't you think they'd notice always being surrounded by walls with no roof?

[Narmoth]

Most of the time, I only tell if it's day or night. Most players wouldn't notice, which kills a bit of the idea. It would be better if they started wondering a bit before.
Maybe throw in sudden day/night changes to make the players notice it

[Lupy]

The cavern walls might be separated from the center by water, which would explain why they don't notice the walls. And the characters, and everyone they meet, will have lived in this huge system of caves (by huge, I mean, the whole world is like this, so easily Eurasia+Africa sized) for their whole lives.

And as I give long descriptions (my players like that), and all of my players are observant people, they will start to notice something is "off" but not precisely what until they get outside.

[kamikasei]

I guess I would ask: why? If they aren't supposed to realize they're underground, then what impact does it have on the game?

It might make an interesting gimmick to build a setting on, but be prepared for the consequences to make the change obvious to the PCs.

[Thurbane]

Sounds a little like the Hollow World of Mystara.

[lsfreak]

You could potentially run into issues with anything capable of flight. Birds and such would probably notice, but have no way of communicating it. Dragons and the like would need to be worked around, since they can fly. Playing using the fly spell might become an issue.

And since I like thinking about these things... what about rain and sunlight and the like? Could precipitation be "leftover" magic, collecting along the ceiling and causing water from the surface to drip down?

[MustacheFart]

I have only one question, will there be smaller, obvious-to-the-players, caves inside this massive chain of caves?

If the answer to my question is no, how would ultimately revealing that they lived their lives in a chain of caves have a significant effect on them when they've never knowingly seen a cave before?

I mean if played in such a campaign, upon stepping out onto the "real world" beach and finding out I had been living in a big cave, I would probably deny this new world as being truly "outside." In fact, I would probably go so far as to assume its some massive spell or illusion created to destroy my home and thus make it my priority to eliminate the illusion and whoever is responsible.

Of course on the other hand, I might just react as follows, "Whoa, we went through so weird opening in a wall and now we are on a beach! This much be an undiscovered part of our world!"

Basically, I agree with pretty much everyone who's posted. I like the idea but you'll need to lead the party into discovering big time, dropping clues early on. If they don't find out they were in a cave until they get outside, how are they supposed to know they are no longer in a cave?

"Well, if we were in a cave, who is to say this isn't a cave? Sure it has a sky but so did our 'cave' of home."

Honestly this reminds me of that old show Lost World.

[Kyouhen]

In the case of flight, I'd suggest having nothing in the caves that is capable of the type of flight that would reveal that they're really in a cave. Your players might sense something is amiss when they realize their characters have been adventuring for months and haven't seen a single bird. And things would quickly become interesting if they used flight themselves and for whatever reason went up to the ceiling.

As for weather, have none. Let your players try to figure out why spells like Call Lightning and Control Weather keep failing. If you really wanted to you could even make it so the vast majority of creatures in the cave would naturally be found in a cave or underground. Let your players try to figure out what they're all doing on the surface and where all the normal surface-dwellers are.

[Lupy]

Hm...

So what if they have caves (the normal kind) within this ubercave?

Also, I see what you mean that I'll have to start dropping hints, but as a plot idea, what if there was a village or some such crushed by stones, and it appeared to be under an open sky? Perhaps the blue of the sky is an illusion? As for weather, there will be constant light breezes from the caves "breathing" and some of the caverns will have water dripping in from the ceiling, causing "rain."

The thing is, I kind of thought that when they got out they wouldn't be affected by the illusion anymore, and would realize that the whole thing is a cave like the ones they went in earlier. Of course, anyone who has never left, (towards the exit things get dangerous) would still see the illusion. What about that?

[Rad]

Sounds a little like the Hollow World of Mystara.

It's nice to see someone that remembers the old days. I was thinking about that too.

[herrhauptmann]

Sorry, from your initial description, I imagine that instead of being in one HUGE cave the size of a continent, they must occasionally go from one cave to another.
Am I reading that wrong?

If the cave system is this huge, might as well make it so that the walls ceiling is miles high.

Would this world of yours be the creation of an epic wizard with a lot of time on his hands (create demiplane epic spell). Or is it just something that exists, with no explanation or purpose whatsoever?

[Hawriel]

If they live in caves the weather would be standard. Call lightning would not be a spell that existed in this world. Or any other spell that wouldnt work in such an environment. There might be some small flying animals like insects, lizards or birds. The characters and the players would know about the ecology of their world as they know it. I would write up a page or to of history and ecology about the world they live in. Put animals, weather, and magic in the world that would be normal. Nothing that would brake the beliefe that they are not in a cave underground. No matter what you do to your world the characters would just eccept it, because thats the way it is, always was, and shall be. They would not know any thing els.

[ghost_warlock]

This idea is giving me flashbacks of the movie Dark City. Mmmmmm...

John: "I don't understand, how can it be night already? What happened to the day? How did I miss it?"
Emma: "You're tired, anything's possible. Get some sleep. We'll straigten up all this tomorrow."

Frank: "Stop playing games on me Murdoch! Stop telling me lies!"
John: "I am not telling you lies!!"
Frank: "Help me out here! Make me understand. I've got this jigsaw puzzle in front of my face and every time I try to rearrange the pieces it still doesn't make any sense!"
John: "What? D'you think it makes any sense to me? I'm as much in the dark here as you are! You'll let me ask you a question. You've heard of a place called Shell Beach?"
Frank: "Sure."
John: "You know how to get there?"
Frank: "Yeah."
John: "Tell me."
Frank: "Right, you take the er, you go to the..."
John: "Where, where'd you go?"
Frank: "Just give me a second will you?"
John: "You can't remember, can you? Don't you think it's kind of odd? Wait, I've got a better one for you. When's the last time you remember doing something during the day? And I'm not talking about some half-forgotten childhood memory, I mean like yesterday? Last week?"

[MustacheFart]

Hm...

So what if they have caves (the normal kind) within this ubercave?

Also, I see what you mean that I'll have to start dropping hints, but as a plot idea, what if there was a village or some such crushed by stones, and it appeared to be under an open sky? Perhaps the blue of the sky is an illusion? As for weather, there will be constant light breezes from the caves "breathing" and some of the caverns will have water dripping in from the ceiling, causing "rain."

The thing is, I kind of thought that when they got out they wouldn't be affected by the illusion anymore, and would realize that the whole thing is a cave like the ones they went in earlier. Of course, anyone who has never left, (towards the exit things get dangerous) would still see the illusion. What about that?

Ya, good stuff. Hints like that will definitely increase the effect your plot twist has on the party.

As far as birds and the "sky" I have an idea. We've all either seen people have dreams on TV or have had them ourselves, where you are running for something but you just can't reach it. It always moves away just as fast as you run towards it. What if the "sky" utilized this too?

Like say a bird is trying to fly straight up and he effectively hits the ceiling. He would still see sky and think he is still heading straight up when in reality he's just flapping away in the same place. Just make the ceiling high enough so that the players don't see the birds flapping in place. Basically a homebrewed version of illusory terrain. I think this could make for some interesting roleplaying if you happened to have more than one party member flying "high" at the same time.

[Fhaolan]

Or it turns into the D&D equivalent of the Truman Show. :)

[Tempest Fennac]

I agree that it would be an interresting setting. I'm not sure why the players would throw books at you over it, though. Maybe there could be a reason for the game taking place underground like some sort of cataclysma with information on it needing to be found once the players reach the surface in order to convince everyone else who's underground that it's safe to go back to the surface.

[bosssmiley]

Sounds a little like the Hollow World of Mystara.

Strange. I thought of the Starship Warden.

[Fhaolan]

The real question that needs to be answered, is why would the characters care? If they've lived in this cave system all their lives, and for many generations as far back as living memory goes... then the conditions in the ubercave would be normal and expected. Skyfall would have happened before, on a regular enough basis that while it's a tragedy, it would be the equivalent to a hurricane. For people well travelled, it would be a known issue.

There's no real shock value to the characters in this scenario to finding out they're living in a cave. They would have no real concept of what 'outside' is. If they leave the cave system, and find themselves on the shore of an astral sea... how is that different from them walking through a portal onto another plane of existence? We as players may know the difference, but the *characters* don't have the metagame knowledge necessary to make that leap.

Not really that long ago humans thought that the sky was a ceiling with little holes in it that let in the light of the heavens. All you're really doing is reducing the scale of that. So, it's really not shocking at all, to the characters.

What this needs is backstory that indicates that this is not normal conditions. That the world wasn't like this originally and it was 'translated' into an ubercave by some cataclysm fairly recently. Only a priviliged few are aware of it officially, but the characters (and others) are starting to figure it out and are asking questions the movers and shakers (literally) don't want to answer.

That would be more shocking, that the entire world was moved into the caves at some point, but it was dressed up so that it wouldn't be noticed at first. That requires *serious* power.

And once the characters reach sufficient levels themselves, adventure hooks around the cataclysm coming back, or simply not being over yet, abound.