Rules for Digging out a Dungeon

[Greenfield]

Yeah, the costs and time schedules presume magic. There's a chart in the PHB for the cost of spellcasting services. It's in the Equipment section.

That's how much it costs to "buy" the magic you need, in the form of skilled professionals.

Also look at the cost of a Lyre of Building, found in the DMG. It's unskilled labor, but by adding skilled labor and/or magic to shore up what the Lyre is excavating.

As for skills, I'd rely heavily on Knowledge Architecture, and I'd set the DC pretty high, since you want to do the excavation without disturbing the structure above. And realistically, even a ground shift of a few inches can collapse a medieval structure.

Of course, realistically, they're going to end up with a collapsed hotel on top of them, but since when does realism come into play?

 

[Hrothgar Rannúlfr]

Thanks, everyone.

This helps a lot!

 

[Summer-Knight925]

I still say digging it should cause some adventure...

 

[Hrothgar Rannúlfr]

Digging it should cause an adventure, for sure.

I almost want to let them think they are starting the dig and then discover that the hotel was built over an old forgotten entrance of a megadungeon, separated from the main dungeon by a secret door/illusion or both, but they accidentally tunnel into it. However, I'm a little worried that such an event might derail the rest of the campaign. But, it'd be worth it if it were fun!

But, I'm not sure that's what they want.

 

[Diamond Cross]

That's the premise of Undermountain.

 

[Greenfield]

Digging it should cause an adventure, for sure.

I almost want to let them think they are starting the dig and then discover that the hotel was built over an old forgotten entrance of a megadungeon, separated from the main dungeon by a secret door/illusion or both, but they accidentally tunnel into it. However, I'm a little worried that such an event might derail the rest of the campaign. But, it'd be worth it if it were fun!

But, I'm not sure that's what they want.

Consider going limp on them.

Let them dig down and discover a "secret" complex of tunnels, foul smelling, rat infested, damp and disgusting.

Let them run around for a while, looking for monsters and treasure, only to discovered they've broken into the city sewer system, and that the only treasures to be found are the ones that fell into chamber pots and wash buckets.

You could add drama by describing the day outside as "foreboding" when they begin, with distant rumbles of thunder and dark clouds rolling in. Then when they're down below, let them face the hazards of being in a sewer when it's raining up above.

Yeah, it's a dirty trick. But after they finish paying their cleaning bills, they may get the idea that they can't just create their own treasure hunt whenever or wherever they want. Sometimes a hole in the ground is just a hole in the ground.