Instead of continuing to hi-jack the other top-hated spells thread, I thought I'd start a thread on spells that allow you to rest. The poster child for this is the Tiny Hut, but there's also Rope Trick and Magnificent Mansion.
Personally, I've never found these too troubling because they're immobile (MM is pretty good, but it's a high level spell) and in no way invisible. Yes, it's handy. It stops random wild animals and scavengers. But set it up in hostile territory in my campaign and you'll probably regret it.
So let's look specifically at (Leomund's) Tiny Hut. The hut is a 10 ft hemisphere. Nothing indicates it has a floor. Spells can't be cast out of or in to the sphere and the caster can't leave the sphere.
So what's the dragon/hobgoblin army/big bad supposed to do when the parties stomps in and uses all their high level spells and then sets up camp? Well I have a few options.
Time
I think this is the biggest factor which plays into the enemies hands and is addressed in more detail for several options. The enemy has up to 8 hours knowing exactly where the invaders are located. That's a lot of time to come up with countermeasures or to make plans.
From below
The easiest is to just find someway to dig underneath. A floor won't stop incorporeal undead or any of the burrowing monsters. Depending on the situation, if the group isn't on the lowest level, the enemy could just collapse the ceiling of the room below.
If the hut is not on hard ground, there's always simply tunneling. See also portable cover.
Portable Cover
So the party is snug in their little hut. The enemy takes half an hour to cobble together some sort of cover. Could be just about anything from an old door or table to some logs hastily strapped together. I once built a functional (well, sort of functional) raft in an hour or so in boy scouts.
Once the enemy has portable cover they can approach the hut without worry. Sure the party can sally forth, but they will be at least 1 man down and not rested. Win for the bad guys.
Since they can get adjacent to the hut, they can now digging underneath, start burying it (at least partially), piling heavy/flammable stuff on top for when the duration expires or any number of other fun shenanigans.
Block off Escape
Okay, so the group is in a good sized room hiding out. The enemy blocks all exits and starves the group out unless they can magically escape.
Run Away
People come to steal your stuff? Run away and take the goodies with you. Buh-bye!
Reinforcements/Ambushes/Traps
Given 8 hours, how many troops can the enemy ready to attack the moment the spell expires? Every cooperative in the dungeon should be getting ready. What would have been multiple encounters now becomes onemultipleencounter.
Preplanned Counters
This one is kind of a catch-all. I assume the bad guys know about spells. Genius level enemies can (sort of) cheat. Assume they thought about this scenario and there are all sorts of nasty things they could have prepared. Some quick thoughts in addition to the above
Others?
- Paint it: have mooks throw jars of paint at the hut until the party can no longer see out. Then do other prep.
- Poison gas: set up poison gas canisters. When the duration expires, flood the area with toxic fumes
- Cage: Have a cage or heavy net that will fit over the hut.
- Flood the Room: Sure they'll be safe in the hut, for a while. Bonus points for flooding the room with acid, flammable liquids or blocking exits.
- Put something hazardous on top: have someone go in invisible and place a whole slew of flammables (or poison or acid) on top of the hut.
- Prep hazardous terrain: Surround the hut with caltrops and ball bearings. Thousands of them if need be. Have a scout ready for when the spell expires and start peppering the group with ranged attacks from behind cover.
I'm sure I've only scratched the surface. What else can you think of that the enemy could do with 8 hours of prep?
EDIT: fixed typo
I'll give you credit for the paint idea trying to negate the party can see out since that is what nullifies most of the "just do...." solutions but not be seen, except for the fact that it ignores how tiny hut works and makes no consideration for the fact that it's a munchkin enabler spell being abused by munchkins.
"Creatures and objects within the dome when you cast this spell can move through it freely" OK Bob, swing ing your shield out through that paint and scrape it off so we can see.... Shield too small? What about this bedroll.
There is also the horrible flaw of reasonableness where you are suggesting painting a ten foot wide dome high enough for a bunch of pcs to stand in without the pcs noticing. Are you painting it with wish? Even tinestop won't give you enough time