#xp grinder

Here's how we get in and out, a bubble column and water drops into a, um, crypt.

There's an exit to the caves. It's very dark in here, just barely spawnproof.

A nice, completely non-suspicious fountain.

The end of the crypt, and a door to a slime chunk. But hang on, what was that opposite the fountain?

... yeah. There might be a big dark space full of skeletons behind that wall. And at the base of Mr Skullface is a trapdoor, which leads to...

A cosy little storeroom where we are, in fact, storing skeletons! This is within 16 blocks of the spawner, so they'll keep coming while I'm here. They get taken up a bubble elevator and then dropped back down to soften 'em up a bit.

If you go down the totally non-suspicious fountain, you find yourself in this little room! It sorts the drops into Bones, Arrows and Other, and I've got my kit for melting down armour, disenchanting gear for XP, and crafting bone blocks and gold bars. The button on the right drains the Other chest of junk into lava, via some redstone that I'm very proud of and built without any googling.