Here are the Veins themselves in order of likelihood. For a crazy slightly gonzo formation you may simply roll a d8
4. War Works
5. Sulphuric blooms
For a more naturalistic generation you can try this table:
13-14. War Works
15-16. Sulphuric blooms
The River is, in real life, the primary creator of caves. It shapes the classic 'wet look' limestone cave with the elaborate speleothems. In reality a river can leave a kind of halo of caves around it, mainly above it as it hollows them out and finds new routes through the stone, but also around, and underneath.
On The Map.
Remember a river will only go down in a vertical section.
Rivers are unlikely to be navigable by boats in real life, in the Veins its your choice. Remember that if ships can navigate a river it makes it extremely valuable and strategically important.
An underground river will be cold, narrow and often fast. Its depth and power will vary tremendously. It will pile over falls and sweep through sumps.
On the Map
The Fault is pretty simple, exactly how you imagine it to look, a jagged line. It doesn’t matter much if it changes its nature or direction when it reaches the vertical sections as it’s the nature of faults to break through vertical space.
A fault could be described as a huge, dry, dark, irregular chasm in the mid-earth. A kind of natural void. Its walls will not be smooth or semi-organic like a limestone cave but rough and fragmentary, bearing the sings of torsion and stress. It may still be moving. It may have tectonic relics. It may still be active. There may be lava.
The Mine is a little like the Fault. The mine heads stop and then a new branch is begun from behind the mine head as the miners seek the vein they are after. Like many of these shapes the mine is an extremely abstracted form of how a mine map would look in real life.
On The Map.
Technically a mine should proceed up and down a little differently than it goes across. I have mainly ignored that though.
The *major* difference between this Vein and any other is that a Mine is rational. It is built to be accessible, though often for races shorter than man. Columns will be left to support the roof. Searching shafts may run in every direction. Dwarves will be able to read the culture of the miners from the toolmarks left on the walls.
(Remember this isn’t an exact map of what the thing does, only where it is. Real rivers and mines can have small falls, steps, ladders, lifts, anything you like.)
War mines are unusual in that you use two colours and that they produce a large amount of lines. If you roll this result you may only need this and one other to make a map. The war works each start in an opposite side of the map and process towards each other.
On The Map.
They essentially look like brush heads. An extending line, then a lateral at its head, then more extenders and so on.
The war works are positioned to cut each other off and intercept each other.
War mines will be smaller and less stable than normal mines. Towards the ‘attack heads’ they will be of a minimal size, about three feet wide and four or five high. They were built fast. There may be signs of conflict. The conflict may still be active. End points may be cut off by explosives or magic collapsing the heads.
The blooms are strands of corrosive gas seeping up from the deep earth, they chemically corrode stone and produce cave systems leading upwards.
On the Map.
On the map the blooms actually look like roses. On the vertical they curve up like stalks, on the top down they are roughly circular infiltrations of corroded stone, like cup stains on paper.
These expulsions ruin the stone. The surfaces are rotted, torn and almost necrotic.
Now we get onto the odd ones. Myco veins represent tendrils of fungus, slowly infiltrating through the stone, cracking it apart, widening it, searching, perhaps blindly, or for some unknown purpose. Then, over centuries, or days, dying back, leaving empty caverns with the rock bearing the strange fungal marks and the passages stretching in gorgonite waves.
On The Map
These are like a very simple tree.
Myco passages will be stained, strange and winding. They may have numerous tiny branching inaccessible pathways. They will however, link up, all products of the same organism they will join like the branches of a strange tree. The cave surfaces may be crumbly like flagstones pushed apart by a mushroom growing from below, or smooth, abraded away by mild organic acids. The passages may still carry fungal smears.
The gigastructure is a built thing. Something huge, a city, ziggeraut or city-sized tomb. It probably wasn't built here, but sank slowly into the earth over millennia, being compressed by the shifting of plates and the slow unfolding of time. Whatever it was has long been forgotten now.
On The Map.
The gigastructure shows layers in the vertical sections and radial pattering in the top-down sections.
Moving through it could be like moving through a giant breakdown pile, except all the stone is worked, blocks, columns, collapsed or tipped over buildings, even sewers or city streets turned on their sides. The cultures will be effaced by time, truly ancient.
A giant *thing* has found its way down from somewhere, an ancient dragon, purple worm, tarresque, mad god or something stranger.
On The Map
The burrow goes laterally across the top down sections and curls in loops down the verticals as the creature digs its way deeper.
Unlike every other Vein, this one has an end. Perhaps the beast still sleeps, or is dead, but maybe not.
The passages have been ripped open by some natural force. The signs of claws or other marks may still be there. The width of the tunnel may give some indicate of the size of the creature.