The wires of a thousand machines have been left to rot and languish in the desert. As time went on these wires were broken into smaller and smaller pieces until eventually, they were but particles of sand. The wind blew it all here. These toxic dunes hardly support any life of their own. The Door in Murex Canyon is a 5th-level adventure for Cairn and B/X in which your team of post-apocalyptic wanderers will traverse a hellish world of rust, toxic smog, and the ruins of an ancient technological utopia. What lies beneath these verdigris sands, and why it was lost in the first place, is a mystery that may be better left unsolved.