A tall mountain range separates the scalding desert in the west from the dripping jungles to the east, and during the Fall a great warlord cut many secret tunnels under them to allow his warmen to attack his enemies in secret. The Shattering broke many of the tunnels but it also cracked the earth below like an egg, so scalding fires from below spat up and coughed into the sky, making new tunnels, until the whole of the smoking mountains were riddled with them.

Now deep in the underlands rockfires still burn and push a great wind through the twisting passageways, warring always with the skybreath from above, and the desert masters use these winds to travel on special kites to the rich fertile jungle realms for plunder, slaves and glory.

Not to be outdone, the hanging towns of the jungles responded in kind with their podboats, so now the mountains are a rat-run of tubes of every size, through which zip various craft at high speed. Grapnel-whips are used to seize upon rocky outcrops on tight corners at high speed.

The dangers are many however, as a wrong turn can force a kite or pod into a narrow pinch, crushing it, the darkness is absolute in many places, a deadwind can fall and leave travellers stranded, the mountain can belch and send superheated poisonous steam spurting through side passages, and enemies can appear out of nowhere armed with long, sharp hooks to disable your craft.

Sometimes the tunnels shift and what was once a safe path might send a voyager high into the sky to plummet to their doom, or be sucked down into a boiling lake or a firepit.

Raiding parties from either side can accidentally meet one another and do battle in the wider tunnels, and legends tell of antiquated metalmen left by the old warlord still clanking around the caverns and ravines, merciless iron claws and ruby-winking eyes reaching out from the shadows.

Pipescouts are celebrated - although usually short lived - and their knowledge of the passageways is priceless. Piperiders, kite pilots, are also cherished as heroes by their tribes, and despite the dangers, competition to join their ranks is fierce. These men and women worship a spirit they call the Red Worm, said to be a goliath monster dwelling deep underground, and they beg it for good fortune on their travels.