"You enter the cave, the wind howling around you," I said. "The cave is not deep, so it doesn't afford much in the way of shelter. In the back of the cave is a door."
"A door?" asked Melissa.
"Yes, an ordinary wooden panelled door. With a handle. It's hinged on this side."
"That's... incongruous," said Carl.
"Out of place, I'd say," said Mike. "The rest of this place seems so bizarre and non-Euclidean."
"Have we seen any other doors like this since we arrived here?" asked Melissa.
"No," I replied. "This is new."
"This is definitely the place that statue directed us to, right?" asked Mike.
"I critted my survival check," said Melissa. "This is definitely the place."
"I guess I open the door," said Carl.
"It opens easily," I said. "It's neither locked nor trapped."
"Oh hey, here's an idea," said Carl. "Let's not open any more doors without checking for traps first."
"Yeah, good idea," said Melissa.
"Beyond the door," I said, "there is a corridor which goes straight ahead as far as you can see. The corridor is clean, lined and paved with hard cobbles and has a vaulted ceiling with exposed wooden beams. There is no dust on the floor. It all looks very well-constructed."
"Oh great, we get a dungeon bash now?" asked Carl
"Oh great! We get a dungeon bash now!" said Mike.
"At least we get out of that storm," observed Melissa. "That was a total pain."
"Yes, this realm has been a pain ever since we arrived," said Carl. "How long ago was that?"
"You estimate that it's been three or four days subjective time," I said. "But it's hard to tell because days and nights don't seem to work the same here."
"Do we even know where here is?" asked Melissa.
"Not really," said Carl. "I assume that it's another plane of existence, but I couldn't tell you which one. It may even be an unlisted demiplane."
"You could roll Arcana to see if you can work it out," I suggested.
"Nah, I don't really care," he replied.
"The door is going to swing shut behind you, unless you want to prop it open with something."
"Is there any light in here?" asked Mike.
"No, once the door shuts it looks like it's going to be completely dark."
"I've got darkvision," said Carl.
"Me too," said Melissa.
"I don't," said Mike. "I'm just a human."
"I have a light spell," said Carl.
"Yeah, but it'd be nice not to put up a bright beacon saying here we are," said Melissa.
"Good point," said Carl. "But I don't see that we have much choice."
"Don't you still have that stone you got from the altar?" asked Melissa.
"Ah! Yes!" cried Mike. "I grab it out of my backpack and set it orbiting."
"Great," I said. "You now benefit from sixty feet of darkvision."
"I told you it'd be useful down the track," said Mike.
"Okay," said Carl. "I shut the door."
"The door shuts with a click," I said. "You are plunged into darkness, though all three of you can see clearly. The noise of the wind outside is suddenly cut off, leaving you in complete silence, which rings in your ears eerily."
"Wait, we can't even hear the storm outside any more?" asked Melissa.
"Nope," I said.
"That's weird," she said.
"Do we still have levels of exhaustion?" asked Mike. "We might need to rest before going on."
"You aren't sure it's safe here," I said.
"Okay, let's see if we can find somewhere that's safe to rest," he replied.
Carl nodded and said, "Yeah, let's head on down this corridor."
"As you move down the corridor, you realise that it ends in a blank wall after seventy feet, just outside of the range of your darkvision when you were standing near the door."
"That's convenient. Almost like it was designed so that we wouldn't be able to see it until the door was closed," said Carl.
"Almost like," I agreed. "At the far end there are two doors, one on either side of the corridor. The doors are just like the first."
"I smell a trap," said Carl. "Let's be cautious."
"Wait here, I say," said Melissa. "I'll go and check it out on my own. Is there anything else in the corridor?"
"No, it's otherwise entirely featureless. The wooden beams are about ten feet off the floor, and the ceiling is a couple of feet higher than that."
"Can I see anything above or on top of the beams?" she asked.
"Only dust," I replied.
"Wait, didn't you say that there wasn't any dust on the floor?"
"I did say that, yes."
"So why is there dust on the top of the beams?" she asked.
"Is someone sweeping it up in here?" asked Carl.
"Or something?" asked Mike.
There was a moment of silence around the table.
"Be very careful," said Carl.
"Okay," said Melissa. "Don't move. I'm going to go very carefully up the corridor, checking very carefully for traps, tripwires, pressure plates or anything like that."
"Okay," I replied. "Roll investigate, with disadvantage because you're exhausted."
"Twelve?" she asked.
"About halfway up the corridor, you're looking in entirely the wrong direction when you feel one of the cobblestones sink slightly under your foot."
"Ah, crap," she said.
"Wait, how far up the corridor is she?" asked Mike.
"The entire corridor is seventy feet long. Your darkvision is sixty feet, so you've moved ten feet from the entrance. Melissa is halfway up, so she's thirty feet from you and thirty feet from the end where the two doors are."
"But we can see the whole length of the corridor now?" he asked.
"Yes," I replied. "You can all see as the wall at the end of the corridor rises into the ceiling, revealing what looks from this distance like a skeleton standing upright. It appears to be carrying a sword."
"And it's sixty feet away?" asked Mike.
"Yes," I replied. "Though it is moving towards you. Melissa, from your perspective closer to it, you can see that the skeleton's feet don't touch the floor."
"Whaaat?" she asked.
"And it doesn't seem to actually be holding the sword."
"Uhhh..."
"Ugh," said Carl. "I hate you."
"I know," I replied. "What are you doing?"
"Rolling initiative, I guess."
"Go for it. Again, with disadvantage because you're exhausted."
"Nine," said Carl.
"Eleven," said Melissa.
"Four," said Mike.
"Okay, Melissa, what are you doing?"
"Can I see what it actually is? Why the skeleton appears to be floating?"
"Make a perception check."
"With disadvantage?"
"Yes," I said. "All your ability checks will be made with disadvantage until you get a chance to rest."
"Fifteen," she said.
"You can now see clearly that it is a cube of some kind of clear gelatinous substance, filling almost the entire corridor. The skeleton and the sword are contained within it, and now that it's only twenty feet away, you can see that the bones and the sword are pitted as though being eaten away by acid."
"You said it's filling almost the entire corridor," she said. "and it's ten feet by ten feet?"
"By ten feet, yes. It doesn't reach up into the vaulted space above the beams."
"Okay, can I leap up into that space?" she asked.
"You can certainly try," I said. "Make an athletics roll."
"Can I use acrobatics instead?"
"Sure," I replied.
"Woah, seventeen," she said. "Even with disadvantage. I rolled a twelve and a nineteen, plus five."
"Nice roll. With a deft flip you leap into the rafters. You're up above it. If it keeps moving up the corridor it'll pass completely beneath you."
"Can I shoot it from up here?" she asked.
"No, that took your action," I answered.
"Okay," she said.
"Carl?"
"I cast freedom of movement," he said, "and I move forward thirty feet."
"Okay, you're pretty much right below Melissa, and twenty feet from the cube."
"Perfect," he said.
"Mike?"
"I go up beside Carl and ready an action to hit it as soon as it enters my range."
"No worries. It does so."
"I hit it. Twelve."
"That hits."
"Eight damage, plus four necrotic," he said.
"Okay. The cube lurches forward and you dig your sword deep into it, leaving a gash like cutting through... well, a cube of jelly. Melissa?"
"I cast hunter's mark and shoot it. Ugh, only nine."
"It's filling the entire corridor. That hits."
"Okay, seven plus five is twelve piercing damage."
"Okay, Carl?" I asked.
"It's right in front of me, yes?"
"Within five feet."
"Okay, I take a deep breath and walk straight into it," he said.
"You what?" cried Melissa.
"While inside, I cast inflict wounds, and then because I have freedom of movement, I walk out the other side."
"That's... innovative," said Melissa.
"Okay, you take ten points of acid damage straight away," I said.
"I can take it," said Carl. "I use my other fourth level spell slot to cast inflict wounds, doing... thirty five points of necrotic damage."
"Woah!" said Mike, impressed.
"Cool trick," I said. "Want to describe what that looks like?"
"Flames, I think," he said. "My body is surrounded by flames drawn from my dark god's hellish realm, which burns it from the inside out."
"It's still alive, inasmuch as a mindless motile cube of jelly can be said to be alive, so make a strength check to escape."
"I have freedom of movement," said Carl.
"You're restrained while contained within the cube, but you can make a strength check to escape despite being restrained. I'll give you advantage on the check for your spell, which cancels out your disadvantage for exhaustion."
"Aargh," he said. "Four," he said.
"You're struggling, but it's got you for now. You can make another try on your next turn. Mike?"
"Can I help him get out?" asked Mike.
"Yes, you can try to pull him out of the cube," I replied.
"No," said Carl. "My whole intent here was to get to the other side. I'll be okay."
"Your call, boss," said Mike. "It's moving slowly, right?"
"Fifteen feet per turn," I said.
"Okay, I'll hit it again, then back off. I want to try and draw it towards me."
"Are you raging?" I asked.
"No," he said. "I don't trust the other guy any more. I assume a sixteen hits. Oh nice! Eleven points of damage, plus five necrotic."
"Okay. It moves towards you, carrying Carl inside it as it does. Carl, you take fifteen more points of acid damage."
"Ow," said Carl.
"Melissa?"
"I drop down behind it and help Carl escape."
"Okay, roll a strength check."
"Thirteen?" she asked.
"That's good enough."
"Can I drag him further back along the corridor?"
"You can drag him ten feet," I said. "Carl?"
"I dedicate my pain to the Dark Lord whose coming I prepare for," he said. "I use my last first level slot to cast cure wounds and get six hit points back."
"Okay," I said. "Mike? It's right in front of you now."
"I hit it again. I get two attacks. Eleven and fourteen."
"Both hit."
"Thirteen slashing damage plus four necrotic total."
"Okay," I said. "You appear to have burst whatever is keeping this thing in its cubical shape, and it sinks and slowly dissolves into a pile of stinky goo."
"Awesome," he said.
"Can I check out the end of the corridor?" asked Melissa.
"Sure," I said. "You can see that there's a ten by ten compartment at the end of the corridor that is completely featureless. It looks like it just exists for storage of the cube."
"So that it is released when someone steps on the pressure plate," said Carl. "A deliberate trap."
"It got at least one person," said Mike. "Does the skeleton look like it has anything useful on it?"
"It's wearing a metal bracer that appears to be undamaged by the cube's acid." I said.
"Great. I grab it."
"Sure. You can identify it at your next rest."
"Speaking of which, we definitely need that now," said Carl. "I'm completely done."
"I guess we need to check these two doors then," said Melissa.
"Check for traps first," said Carl.
"Roll investigate," I said. "Once for each door."
"Three and five," said Melissa. "I hate being exhausted."
"They look safe," I said.
"Okay, I open the one on the left."
"Make a Charisma save."
"Eleven," she said, wincing in anticipation.
"Who's closest to Melissa right now?" I asked.
"That'd probably be me," said Carl.
"Yeah," Mike agreed. "I'm still further up the corridor."
"Beyond the door you see an infinite gulf of black, a space shot through with darting colours and with tiny glittering points of multicoloured light in the distance. There is no floor or walls or ceiling, but that hasn't stopped Melissa from trying to step out into it. You've had to grab her and hold her back while she tries desperately to throw herself into the void."
"Oh, this'll be fun," said Melissa.