OP, one of the great things about Valheim building is 99% of your materials are recyclable (not the stone required for earthen walls though).
This means you can easily try stuff out then knock it down it you don't like it or if it needs an upgrade that requires a clean slate. My personal favorite is to integrate/blend my construction into existing features.

Originally posted by Renlish:

FYI, there are mods that allow you to build in all the instance aspects of the game (ie, caves, crypts, etc) if you really want to. It's kinda fun and cool.

Honestly, that would be kinda neat.

Not sure about Burial Chambers, Crypts, or Mountain Caves.. but Troll Caves could certainly be made as makeshift smelting bases at least.

Still hope we get a proper Cave system-type biome at some point. Maybe have to fight Jörmungandr as the biome boss.

Thank you all for the replies! It's a bummer one can't make a home within a dungeon area (awesome that there are mods for it though), and thank you for the tip about the cave entrance and it's uses! @Eightball yeah, that was my thought too, to have a kind of raid free area with a pleasant little loading screen wall to identify home and the wilds. I tried, but like Fzanco said, it's unfortunately not possible to build a work bench inside the cave. And thank you for the spawn information, good to know I can clear a dungeon and keep it that way.
Thank you us271 for the spawn information and what can be placed inside! I actually ended up using the mouth of a troll cave as a "wall" for my first water side, double story house (now if only I know how to support the roof better)!
Thanks for the tips, Science Dog and Fazanco! I didn't think about using it as a minimalist shelter space, that's awesome! I'm using the water front house as an outpost close to the trader, but will definitely make more, smaller outposts using mouths of caves.

FYI, there are mods that allow you to build in all the instance aspects of the game (ie, caves, crypts, etc) if you really want to. It's kinda fun and cool.

Not sure if it is still possible, but used to be able to dig under them.

I like to place a fire just before you zone in to the troll cave because that spot provides shelter and, with the fire there, you can get a 10 min rested bonus. Helps me keep my rested bonus for better stam regeneration while I'm on the move. Never tried making anything long-term with a troll cave, though.

Hope this helps!

You can't build in them except a fire and cooking station, there may be some other misc items like gold piles. But a troll cave entrance is a wonderful free shelter, you can fit everything you need under it, bed, fire, workbench, forge and max comfort items, it's awesome

Caves and crypts will not repopulate once cleared unless they had a 'generator' and you left it standing (for example the purple smoking bone piles in crypts).

The troll cave should be fine as no troll will spawn inside BUT I don't know if a workbench inside the cave would prevent a troll from spawning outside the little cave 'instance' so let me know if it seems to work.

Never actually tried to build inside one; can you even place a workbench? if you can it is kind of a neat idea and would be immune to raids.

Caves and crypts do not respawn anything internally except the yellow mushrooms. The Black Forest crypts will respawn one external guard after the initial 3 are killed. Both caves and crypts are limited to campfire, sitting log and cooking station as far as things you can put in them. They make a good resting spot if it's night and you're not ready for nocturnal mobs. The external stones they are made of are indestructible and some players integrate them into a base. Use your imagination for some cool creations.