So I've got a couple of ghosts. And they are attacking one of the vampires I have walled away for safety sake (we don't have the heart to kill them, they were once our friends). What can I do to get rid of the ghosts?
The only way to settle a ghost is to inter the corpse. But what if the body has been destroyed or is inaccessible?
Making slabs is a two-step process. First, get a mason to make a blank slab at a Mason's Workshop. Second, get an Engraver to carve a slab at a Craftsdwarf's workshop.
Finally, build the slab just as you would a grave.
As long as it remains standing (and it should, unless something crazy, like Magma, intervenes) the ghost will remain placated, and bother your dwarves no more.