I found a Giant Spider dungeon up inside a mountain once, made a nice drop-to-kill string grinder out of it.
If you're trying to keep the Spawn area as natural-looking as possible on the surface, as long as you light everything up well with torches, you can bury just about everything you'd need to build underground, no problem. I used to build quite extensive underground bases inside mountains, and aside from a few entrance/exit areas and the odd skylight for old-style villages or beacons, I modified the terrain above ground as little as possible. And yes, these included darkroom-based mob/item grinders with a drop-to-kill mechanism (later supplemented with a lava blade once they started letting skeletons and zombies spawn with Feather Fall 4 enchanted armor).
And if you're building extensive underground facilities...you'll eventually break into most of the caves nearby anyways. Just make sure you loot and light them extensively and don't leave spawnable dark areas inside them. So the caves aren't the problem when it comes to spawning rates. Lighting up the surface with a crapload of torches is gonna be more of a problem, especially on uneven ground. And, these days, lighting up the surface includes the seafloor and riverbeds due to Drowned.
Rollback Post to RevisionRollBack
"I think I'm starting to like this `programming' thing. It's about four times as fun as shaving." -- Notch, June 12, 2011
If you don't like having the surroundings all lit up you could just settle for having the spawner work during the day.
Though if you've got an ocean or deep river nearby the water would keep the drowned from despawning due to the light of day so you might have to do something about them.
looking for a mob drop design inside a mountain, would like to keep the area around spawn looking natural , no big platforms in the sky.
The design would be pretty much the same, just that you have to dig it out instead of building it up.
Plus, of course, that you'd have to light up or fill a lot of caves out to 128 blocks from your AFK position to get a good yield from it.
An alternative for the most common mobs would be finding cage spawners since they only check their mob caps in the volume right next to themselves.
Just testing.
Per my discussion with Hexalobular elsewhere, this mob spawner will likely not be very effective for reasons he's given.
Especially just the fact that you have to compete with so much surrounding spawn area.
Though a mountain would have less room for caves than flat land, if it's a tall mountain and you build near the top anyway.
And AFK'ing above it would cut that down even more, only needing a small platform in the sky.
Just testing.
I found a Giant Spider dungeon up inside a mountain once, made a nice drop-to-kill string grinder out of it.
If you're trying to keep the Spawn area as natural-looking as possible on the surface, as long as you light everything up well with torches, you can bury just about everything you'd need to build underground, no problem. I used to build quite extensive underground bases inside mountains, and aside from a few entrance/exit areas and the odd skylight for old-style villages or beacons, I modified the terrain above ground as little as possible. And yes, these included darkroom-based mob/item grinders with a drop-to-kill mechanism (later supplemented with a lava blade once they started letting skeletons and zombies spawn with Feather Fall 4 enchanted armor).
And if you're building extensive underground facilities...you'll eventually break into most of the caves nearby anyways. Just make sure you loot and light them extensively and don't leave spawnable dark areas inside them. So the caves aren't the problem when it comes to spawning rates. Lighting up the surface with a crapload of torches is gonna be more of a problem, especially on uneven ground. And, these days, lighting up the surface includes the seafloor and riverbeds due to Drowned.
If you don't like having the surroundings all lit up you could just settle for having the spawner work during the day.
Though if you've got an ocean or deep river nearby the water would keep the drowned from despawning due to the light of day so you might have to do something about them.
Just testing.