The scrap heap of the planes, Thuldanin is the second layer of Acheron, and home to creations both worthless and wondrous from across reality. Here is the land after war has finished, after conflict has ended, after there is nothing and no one left to fight; civilization gone, sword spirits roaming empty battlefields, and all that remains the creations of lost armies, of collapsed nations slowly breaking down, transmuting to lifeless metal and stone.
The exterior of the cubes of Thuldanin is chilled, even the most crowded cubes feeling the cold of a lone cube of Avalas, though here the plane's natural properties bring about blizzards of iron flakes, not snow. As such, most visitors to Thuldanin keep within, for the cubes of the layer are pockmarked with pits and tunnels, the deepest of which lead into the interior of its cubes: vast realms containing nothing but old machines and constructs, devices of war and devices of convenience alike filling the hollows, near all long since petrified by its magics. This petrification can be a danger for any who remain here too long, as it effects everything within this layer, both living and not. As a result, this layer is almost entirely uninhabited; there is no native life of any sort within Thuldanin, only the occasional migrant from Avalas (often rust monsters feeding on ferrified trash), and the only significant long-term community is the refugee duergar of Hammergrim, where Laduguer protects his people from the encroachment of Thuldanin.
The preservative nature of Thuldanin means that any item, object, or being on this plane has a cumulative 1% chance per day for every day beyond 30 of turning to the same iron-like stone that composes the cubes of Acheron; leaving Thuldanin resets this. Items so transformed lose all magical properties, though they can be restored to their original composition (and functioning, if technological) with a dispel magic cast against CL 20. On living creatures, however, the layer's petrification can only be reversed by powerful magic on the order of a wish or miracle spell. Rust monsters and rust dragons are immune to this effect.
- Doors to the Unknown, pg.29
- Manual of the Planes, pp.126-127
- Planes of Law - Acheron, pg.21
- Planes of Law - A Player's Guide to Law, pp.10-12
- Planescape Monstrous Compendium Appendix II, pg.102