What version are you playing?
This could be one instance of the pathfinding bug, though never seen it this way. Try locking an unlocking door or saving / reloading to see if the problem vanishes.
Tried that, and reloading. No good.
I read somewhere that having two depots causes problems (the wiki perhaps?). In any case as far as I know only one will ever be used at a time. I think I've heard of people having two on map - normally with one as an elf trap, but I don't know what issues there might be, or what you have to bear in mind for that to work. So, I'd say just use one.
THe problem, as far as I know, coming from two depots is that part of the caravan could end up in one and rest of it to other depot. As the caravan is spread in two or more depots, the game thinks the caravan has never arrived, and trading is not possible
I had a third depot up near the surface and it was listed as accessible, though I had destroyed it as I have these two.
I read somewhere that having two depots causes problems (the wiki perhaps?). In any case as far as I know only one will ever be used at a time. I think I've heard of people having two on map - normally with one as an elf trap, but I don't know what issues there might be, or what you have to bear in mind for that to work. So, I'd say just use one.
That said I could well be wrong; I often am.
Why are you using two anyway? Just for the aesthetics?
One's going to be set up to a drowning trap, the other stocked with delightfully shiny trading goods.
Still, worth checking -- blow apart the 'good' depot, is the other one now accessible?
As soon as I can get a mason out there I will; there's a large ambush coming. ^^
EDIT: Dismantled the working depot, the other is still not accessible.
EDIT 2: Dismantled both depots and rebuilt them while the terrain said it was okay. Now they're ALL inaccessible. GENTLY CARESS