D&D 5E seeking the Logical and Scientific for help with dungeon creation

[bluey the bard]

Let me preface this by saying I am one of those "creative people." I know, gross. My mind will latch onto a delightful idea I invariably think up whilst expunging waste into my bathroom's crap receptacle, but then I'll be hamstrung by a desire for things to actually make sense. I have a very strong distaste for the explanation "um, it's because, uh, um, magic." to compensate for a deplorable lack of forethought.
Anyways, here's the pitch.
In an upcoming campaign I will be running, I have a location that will end up being the focal point for the "story". Again, I know, gross. This location is loosely based on Predjama Castle and the connected Postojna Cave. Basically, it's a castle built into the side of a rocky hill and there's a connected cave. However, I want this hill (or mountain) and local cavern to be formed over and around the body of a dragon. I think this sounds cool. An enormous dragon, eternally asleep, encased in the very stone of an ancient grotto? Totally epic.
But then the logic kicks in. How would a giant dragon become covered in rock, and how would a cave form around and under it? I attempted to do a bit of research on cave formations, as it turns out Postojna Cave is a karst, created by the flow of a river. Seeing as mountains and hills can take thousands to hundreds of thousands to millions of years to form, can I get some suggestions for how this might work? I'd like to keep the formation of this landmark within a time span of a few thousand years.
Thanks in advance for any and all comments.
To clarify, I'm asking for help with the technical and scientific aspect of this, not a barrage of "that's the dumbest thing I've ever heard of" replies.

 

[Imaculata]

Maybe the grotto was once the dragon's lair, but it collapsed over time? The dragon simply didn't notice, because it is in hibernation. And I would presume that no one knows the dragon is still alive, or else it would probably be the last place you'd want to build a castle.

Alternatively, maybe the cliff is actually an ancient exploded volcano. It exploded a long time ago, and one half of it crumbled into the sea. The dragon was simply asleep inside the volcano, and ignored all the seismic activity. Maybe the seismic activity was actually the result of the dragon gently tossing and turning in its sleep? Either way, that dragon would have to be pretty deep asleep for people to build a castle near it.

 

[Voi_D_ragon]

What if the dragon is imprisoned there? If I recall correctly, there is a 9th level that encases you in a force field and buries you underground. Another option of that spell is an unbreakable magical slumber, so maybe the ultra Arch-mage of ages past was able to combine the two effects on the greatest Wyrm of his time, saving civilization bla bla, but the spell is slowly unraveling, if you want, or else you can just let it sleep forever.

 

[MarkB]

If you want to look in terms of anything shorter than, well, literally geological timescales, and you don't want to just say "because magic", then you're probably going to have to look in terms of major geological upheavals - ones which can geologically reshape a region relatively quickly.

Mostly that's going to mean earthquakes or volcanoes.

You didn't specify what type of dragon this is, and I don't know how flexible your concept is, but one option would be for it to be a classic fire-breathing type (red or gold) that prefers hot, volcanic environments. Work in 5e's concept of legendary creatures influencing the region they make their home, and any region this dragon sets up shop in will become hot and volcanic.

So, maybe thousands of years ago, the dragon was hit by something like a Medusa's gaze, and petrified to stone. With the dragon 'dead', its volcanic lair went into meltdown, erupted, and encased it molten rock. Without the dragon's influence, the region eventually reverted from its unnatural volcanic state and went back to the more stable condition of its normal geology.

The petrification should have been permanent, but perhaps due to the dragon's innately-magical nature or some protective magics it had, or maybe due to changes in the natural flow of magic in the region, it's recently begun to gradually wear off, the dragon's body slowly reverting from stone to living flesh from the inside out.

Bonus points if parts of the castle and grotto have actually been carved into some of the less-vital portions of the dragon's body, or formed from stone quarried out of its outer hide. Imagine the shock and embarrassment when a portion of the dining hall reverts to flesh in the middle of a grand banquet.

Still somewhat "because magic", I know, but hey, it's a dragon.

 

[Lanliss]

my 2cp

1) Dragon finds convenient chasm, nestles in like a cat in a box. Dragon-Foe finds dragon asleep and vulnerable, uses spell/poison to keep dragon asleep, and construct the castle above to hold vigil over Dragon.

2)Dragon wanted a nice claustrophobic place to sleep, and buried itself for its hibernation, banking on the miles of stone protecting it against attack during its vulnerable Hibernation period.

3) Dragon rolled over in its sleep, too big to consider the caved in grotto a problem (make it a big enough dragon and the stones would be like sprinkles of dust, or crumbs).

4) "Dragon" is a myth, or left long ago by tunneling down to the underdark. More interesting if this fact is learned when the heroes NEED a Dragon Heart to save the Kingdom, and thus begins the hunt for Dragon.

 

[LordEntrails]

Note, not all caves take thousands of years to form. Think of sinkholes caused by limestone erosion. They can happen in just years when a limestone formation is exposed to underground water.

So, maybe the caves were caused by the dragon urinating or bleeding or diverting a stream.

Next, is this a "real" dragon? If so, how big? Because even a really big one is only 50?? feet tall and maybe a few hundred feet long when stretched out. So, maybe the "dragon" is actually just curled up around one or two of the towers?

 

[Quickleaf]

Let me preface this by saying I am one of those "creative people." I know, gross. My mind will latch onto a delightful idea I invariably think up whilst expunging waste into my bathroom's crap receptacle, but then I'll be hamstrung by a desire for things to actually make sense. I have a very strong distaste for the explanation "um, it's because, uh, um, magic." to compensate for a deplorable lack of forethought.
Anyways, here's the pitch.
In an upcoming campaign I will be running, I have a location that will end up being the focal point for the "story". Again, I know, gross. This location is loosely based on Predjama Castle and the connected Postojna Cave. Basically, it's a castle built into the side of a rocky hill and there's a connected cave. However, I want this hill (or mountain) and local cavern to be formed over and around the body of a dragon. I think this sounds cool. An enormous dragon, eternally asleep, encased in the very stone of an ancient grotto? Totally epic.
But then the logic kicks in. How would a giant dragon become covered in rock, and how would a cave form around and under it? I attempted to do a bit of research on cave formations, as it turns out Postojna Cave is a karst, created by the flow of a river. Seeing as mountains and hills can take thousands to hundreds of thousands to millions of years to form, can I get some suggestions for how this might work? I'd like to keep the formation of this landmark within a time span of a few thousand years.
Thanks in advance for any and all comments.
To clarify, I'm asking for help with the technical and scientific aspect of this, not a barrage of "that's the dumbest thing I've ever heard of" replies.

Welcome to ENWorld

There's a link in my sig about dungeon creation that may be of interest to you.

I'll try to be scientific in my answer, but it's very likely that you'll end up with something like "the dragon sent into an eternal slumber by the sorceress stirred periodically in its nightmarish sleep, and in these stirrings the ground churned and soft rock fell away, forming the caverns of INSERT NAME HERE."

A karst takes a long time to form, you're right, and probably longer than your timeline of a few thousand years. Not all caves are karsts, however. While water is generally involved in the creation of most caves, there is a theory that some caves form more rapidly from sulfuric acid dissolution. For example, the Guadaloupe Mountains of southeastern New Mexico and west Texas were at least in part formed by sulfuric acid. Think Carlsbad Caverns and Lechuguilla Cave.

Carlsbad Caverns (a cave system formed at least in part by sulfuric acid dissolution) may not quite the same look as Postojna, but it's not radically different. The sulfuric acid dissolves limestone but leaves behind gypsum.

There was a NOVA program called The Mysterious Life of Caves that I recommend. Honestly, there's a LOT we don't know about how caves form and how much time it takes them to form.

EDIT: And back to D&D, maybe your ancient dragon bleeds sulfuric acid? And when it went to ground after being wounded, its blood formed the caverns?

 

[Oofta]

Is it a dragon? Or a dragon demi-god? Is it a dragon that was or a dragon that is yet to be?

In addition to the excellent ideas above, another option is that it is a dragon that is forming from some primordial dragon spirit. The stone is slowly transforming stone deep inside the mountain from inanimate rock to a new dragon god's avatar. As it becomes more and more dragon-like the caves vent more steam and sulfur along with increasing tremors.

There were many superstitions and myths around creatures forming spontaneously from inanimate materials.

 

[ccs]

I would imagine that your dragon became covered in rock & rendered unconscious after an epic fight so long ago that it's now just a myth meant to explain why the areas called the Dragon Spine mountains or such.

As for the cave(s)? Well, somebody didn't believe that it was just a myth....
The tunnels, caves, & the castle? That's the result of those somebodies mining their way to the dragon. The cave network has expanded over the years as the miners have stripped the scales & flesh, maybe even claws, off of sections of the beast.
Or maybe they're trying to excavate/free/raise the dragon!
Heck, these somebodies might even be long gone/vanquished & now their castle (& it's secret excavations) are controlled by somebody else - who has no idea. Until the trouble starts.

The castle should definitely be named after the dragon. Castle ______.

 

[freeWeemsy]

Maybe there is some volcanic activity that happened nearby that created a massive lava flow a long time ago. Maybe there was a dragon that was flying near the volcano that was injured by the eruption and lost the ability to fly. You could make this dragon say a blue dragon that in an attempt to save itself it started freezing lava as it was rolling over him. The dragon was just able to stop the flowing lava from covering him, but it resulted in him being entombed in a rocky prison.