Subangea is a giantic cave that stretches below the surface through endless cavities. From oil oceans to volcanic sinkholes and even upside-down forests, the environment is ever changing from one cavity to the other.
So is the fauna except for one small detail, it is always trying to eat, dismember you or simply ram into you. All kinds of species of monsters living in all kinds of conditions and they are all trying to kill you to survive.
But no matter how big or venomous or fire-breathing, men and women will stand to slay those monsters and gather their valuable parts. They are hunters.
In the shining light of the glass roofs or within the blackest obscurity of the tunnels, they draw their powerful swords to... Wait, where are the swords ? The ore shipment was supposed to arrive yesterday ! The trading route with the dwarfs from the volcanic sinkhole is too long and dangerous and without new weapons the fields won't be safe from the monsters for long.
Legends tell that past the ice cave in the north lies a tunnel that leads directly to the volcanic sinkhole. The city scientists say it is pure folly, the wind would engulf in and blow anyone trying to get through or the tunnel would simply not handle the heat difference or- WHATEVER ! We need the dwarf's ore if we are to keep the beasts away !
Setting with a group of adventurer through out the caves to the frozen cave, you finally catch a glimpse of it through the blizzard: The legendary Mifrost.
Excitation runs through your veins and you run towards it to see... What exactly ? A half-frozen half-molten path in the rock ? A collapsed pan of the cave ? A gale so strong you get sucked in ?
The frozen cave is a 5km x 10km cavity with ice ceiling in which temperatures go from -10°C to -40°C. It runs under permafrost ground.
The volcanic sinkhole is a 5km radius cavity with high volcanic activity in which temperatures go from 45°C to 60°C. It is sitting on a hot spot and has vents on the ceiling from which gas and hot air can evacuate.
The tunnel is 65km long and connects the two caves. The first half is subject to volcanic activity and the second half is cooled down by water streams from the ocean.