"Demons live in very deep caverns?  - In stories.  Much deeper than this one."

"Huh, I'd been under the impression that there were no local demon stories. I'm not from a cavern; I'm not from this universe at all."

"Wow!!  - I know a lot about old underground niche stories."

"If you recommend me some books I will set about having them translated. How cold does it get if you go in deeper?"

"I didn't go too far, but I wouldn't have landed in a cavern so close to the antarctic celestum on purpose because it's supposed to be very."

"I guess I'll go in and check myself. I wonder how far in this goes." Does a laser measurer hazard a guess if he aims one in?

It's too far.

"Can I come?"

"If you wanna put on a heavy duty coat I guess you can!"

"I don't have one."

"...yeah, so, if you're coming, I would provide you with cold weather gear."

Isaac dances for two and a half seconds about that, striking a few poses and footworkily bouncing between them.  "Thanks!  Can you make it lucky for me?  Can you make it so it can go under my windbreaker?  My windbreaker is so excellent and deserves to be displayed on the outside."

"I don't think I can make it lucky on purpose though I have no particular reason to believe it would interfere with whatever process normally makes things lucky for you. If your windbreaker is roomy enough to go on top of a large coat I don't see why not."

"My beloved and perfect windbreaker is a little snug."

"Then tragically it will not fit over any properly insulatory coat."

"We'll work something else out, then."  (Exclusive 'we', Felicity notes.)

"If you say so." How rough is the terrain in the floor of this cave?

Pretty rough.

"I think I should fly further in rather than making a ground vehicle, so I guess you could stay in the shuttle when it gets too cold for you." He heads back to his shuttle.

"Okay!"  Isaac trots in behind and almost starts running his hands along things before firmly putting them behind his back and holding them there.

And Felicity follows.

"If you want to pet my shuttle it's not gonna break," snorts Cam, and it lifts off and enters deeper into the cave.

"Cool!" he exclaims in Englatin, and pets the shuttle a few times before turning to a more investigative kind of touching.

The shuttle has almost no mechanical controls at all and just responds to Cam's chip; it glides into the cave. Cam turns on its lights.

The cave may or may not have obvious differences from caves Cam is used to depending on how used to caves Cam is.  Isaac switches to watching out the window and occasionally sneaking glances at Felicity and Cam once he's done looking around and touching things.

The temperature stays mostly the same, trending slightly cooler, until they approach a bit of cavern way bigger than they'd previously flown through.  At which point it promptly drops well below human-comfortable temperatures.

"Huh, pretty sudden drop in the temperature hereabouts. Is there something Polaris-ish that sticks under the surface of the world up top?"