Why dungeons, and where do they come from?
Dungeons are the staple of fantasy role playing games, but actually represent a number of different options. Dungeons provide an easily enclosed environment for the Dungeon Master to run adventures in. Dungeons only have to be as big as the DM wants. Making things easier for the Dungeon Master though is not really sufficient reason for lots of dungeons to exist. Dungeons have to have a rationale that fits the overall gaming world.
Dungeons are expensive to construct, and cost the same to maintain as a castle or similar. So why don’t people build castles instead of dungeons? In a non-fantasy world, castles are very tough to attack. The shear walls and battlements make entrance very difficult, and make defense very easy. In a fantasy world, things are different. Magic spells can more easily level a wall, and destroy a castle. A dungeon is tougher to destroy since so much of it is underground. A mage can block an entrance or two, but still won’t be able to get at the people and goods that might be trapped. The mage can not always be sure that there are not more ways out also. Castles are vulnerable to flying attacks, and much more powerful long-range magical attacks. This is similar in some ways to the invention of gunpowder. Magical flying can drop an enemy force inside the walls of a castle very quickly, or area attacks such as fireball can be used to clear the grounds inside a castle very quickly. While fireballs and such can do great damage in a dungeon, they can only effect a small area due the confined nature of dungeons. In summary, dungeons offer more in-depth protection than a castle. The castle is a very good defensive layout against most raiders such as Orcs or bandits, but fails against more determined foes.
Dungeons come from a number of sources. The source will determine how extensive and dangerous the dungeon is.
The first, and most typical, is the underground hideaway of high level magician or similar. High level magicians and illusionists will build a hidden lab to practice magic in. They do not want to be disturbed by either local authorities or by wandering people. In some societies there will be a college of magic that sponsor’s research, but magic user dungeons are still needed for the most dangerous magical research. The underground magic lab may be occupied or abandoned. If it’s abandoned, the most common cause is the death of the mage who built it. The mage might have died of old age, magic gone awry or been killed by invaders.
Second is the abandoned stronghold. Clerics and fighters will found a village or town and build a castle. As part of the castle’s protections there will be a dungeon. The castle dungeon provides a place of safety in case of attack, a place to store valuables and ordinary things and a place for the guards to live and eat. Castles will become abandoned from being on the losing side of a war, being ransacked by raiders, or abandoned by changes in economics. Losing a war will usually result in the destruction of the castle during the war. The winner may not rebuild the castle if they don’t want to occupy the land. Raiders will sack a castle and kill the inhabitants. The village and castle is likely not to be resettled unless most of the original villagers and the nobleman live through the raid. Changes in economics will cause a town and castle to be abandoned. The people will move to other areas that are more advantages. This is especially likely to happen with a fighter who fails to return from an adventure or their grandkids run out of money to support the castle and buy outside goods.
Third is the abandoned mine. A mine in and of itself is no big deal. Mines that are abandoned tend to become refuges for monsters, thieves or bandits depending upon how far the mine is from a city or other important location.
Fourth is the lost city. Cities can be lost for a number of reasons. First, the city could be destroyed by a natural disaster such as Pompeii was. While volcanoes are relatively rare, mudslides and floods are not rare. It is very possible that mud would engulf a city, town or even part of a city. On Spire, and most fantasy worlds, another common means of creating lost cities is encroaching monsters overrun them. They don’t have to be regular monsters, they could be an invading army or similar. Spire is susceptible to having remote villages also being abandoned. When a resource gives out, or there are too many monsters or bandits between the town and the rest of the world, the town is abandoned.
Fifth is the natural cave complex. This is common in areas that are mixtures of hard rocks such as granite and soft rocks like limestone. Water will wear away the limestone leaving a random cave system. Often these systems will have many entrances and can cover hundreds of miles underground. This is common the Pennsylvania and parts of western Virginia.
Sixth are the dungeons that exist inside existing cities. This is seen in Paris and Rome. In Paris the city is built on top of old quarries. As the city grew, it needed rock for building, especially marble. Each time the marble pits are built on the edge of the existing city. As the city expands, they build on top of the quarries and build new marble pits on the new edge of town. In Rome, the catacombs are on the edge of town to serve as cemeteries. People do not want to travel a great distance to bury their dead, nor can they afford large expanses of land for burial sites. Instead, they build catacombs underground. As one set of excavations gets full, they dig deeper and further afield from the entrance. The digging is semi-random. Each section has a plan, but there is no overall plan for the entire catacomb. Digging follows the soft rock, plus the need to create crypts for the bodies. Eventually many of the catacombs on the edges of the city will merge together underground. The other kind of dungeon under a city comes from build up of the city streets. Streets are not kept at the same level. As garbage builds up, the street gets higher. This is a gradual process, such that most people don’t directly realize it. People will build a new entrance to their house or store instead of clearing the street. Clearing the street would most likely result in flooding since the city or the residents would not clear most of the other streets. The dungeon consists mostly of basements of old buildings, the sewer drains and similar.
Seventh are the dungeons underneath temple complexes. These dungeons are usually dug to bury the bodies of important people, hide and protect treasure or provide safe place for worshippers to congregate. If the complex is not abandoned there could still be filled with treasures from the dead or just treasures of the temple. Another use is to provide a refuge for a monster / god that must be appeased to prevent troubles. This would be similar to the Minator from ancient Greece, or from Battle Circle or from Tombs of Atuan.