Monica Almeida/The New York Times
TECATE, Calif., Dec. 6 — The tunnel opening cut into the floor of a shipping container here drops three levels, each accessible by ladders, first a metal one and then two others fashioned from wood pallets. The tunnel stretches 1,300 feet to the south, crossing the Mexican border some 50 feet below ground and proceeding to a sky-blue office building in sight of the steel-plated border fence.
Three or four feet wide and six feet high, the passageway is illuminated by compact fluorescent bulbs (wired to the Mexican side), supported by carefully placed wooden beams and kept dry by two pumps. The neatly squared walls, carved through solid rock, bear the signs of engineering skill and professional drilling tools.
Most of the tunnels are of the “gopher” variety, dug quickly and probably by small-time smugglers who may be engaged in moving either people or limited amounts of drugs across the border. But more than a dozen have been fairly elaborate affairs like this one, with lighting, drainage, ventilation, pulleys for moving loads and other features that point to big spending by drug cartels. Engineers have clearly been consulted in the construction of these detailed corridors.
While a 1300' tunnel isn't exactly an 'Underground World', the idea does have some possibilities to it. What would a more complicated underground complex dedicated to smuggling look like? Where would such a complex be located? What would its inhabitants be like?
1)Where are smuggling tunnels found? Smuggling takes place where some commodity or service is cheaper on one side of a border of some sort, and profit can be made by selling it on the pricier side of the border. Once it's across the border, further smuggling tunnels/complexes/methods may be used to continue the commodity's journey to the center of maximum profit for the smuggler.
Top places to find smuggling tunnels in the real world today are places like the US/Mexico border - there are people who want to cross, and there is also a commodity (drugs) which is easier/cheaper to produce on the Mexican side and smuggle across than it is to produce on the 'denied' US side of the border. Another place smuggling tunnels may be found today is on the Egypt/Gaza Strip border, where weapons and other denied goods that can be obtained in Egypt are smuggled into Gaza. These borders are not 100% hostile, but neither are they tension-free.
2)What is being transported? You name it. Drugs, money, people (with or without their consent), weapons, and other goods get smuggled through a variety of means. Perhaps in a fantasy setting, monsters that have been eradicated and outlawed in a peaceful kingdom are smuggled in for underground bloodsport arenas. Deep elves pay handsomely for surface elves captured and transported below as slaves. Salt is taxed heavily in one kingdom but plentiful next door, and the salt mines connect directly to passages that circumvent the border.
3)What features might a smuggler's complex have? Well, for starters, its about transportation, so there will be systems of pulleys, tracks, elevators, slides, and other means of conveying things from one part of the complex to another with relative ease. Even so, a smuggler must be able to stop things getting from one place to another too easily when law enforcement (or delvers!) show up, so any such transport system will be peppered with defenses, traps, diversions, false pathways, and portions which can be shut off by the complex's controllers. It will have hidden entrances at least on the denied side (but probably on both sides), and may have 'dead drops' for cargo so that suppliers or customers never actually come face to face with the smugglers.
If the complex is inside a borderland mountain, it might have lookout towers on both sides of the border, to warn of pending invasion on the denied side and of incoming shipments on the production side. It might also contain warehouses for storing goods, housing areas for the smugglers (or any living traffic). It might have communication systems of speaking tubes built in to allow various parts of the complex to coordinate moving goods or people. If the complex ever falls into disuse and becomes inhabited by other denizens, these features will still make it distinct from other subterranean complexes. The speaking tubes may instead be used for taunting other denizens, and controlling the chokepoints in the transportation system will always indicate who the real powerholders are.
Am I forgetting anything?