The original roleplaying game, 1974’s Dungeons & Dragons, set the template for a hugely popular genre that persists to this day as RPGs, boardgames (such as Descent) and video games (such as World of Warcraft). The core activity in these games is to enter underground complexes of rooms and tunnels (dungeons), defeat their various inhabitants (dragons, if you’re out of luck) and steal their treasure. The player characters who do this are termed adventurers – or, by some these days, murder hobos.
As you may have noticed, there are very few dungeon-like sites in the real world, and real people who behave like D&D adventurers tend to have extremely short careers. Let’s ignore the murder hobos and look at dungeons from an archaeological perspective, to investigate why they are never seen on Earth.
A typical D&D dungeon is located just beyond the edge of a tract of wilderness, at a convenient commuting distance from a friendly settlement such as a semi-isolated farming hamlet. The first question for an archaeologist is whether the dungeon is inhabited by sentient living creatures. If not, it is either an animal warren (basically a very large anthill) or a tomb.
Apart from magpies, animals aren’t interested in collecting treasures. So let’s look at a tomb. A dungeon is always full of treasure when the player characters reach it, which means that the tomb must be extremely well hidden and unknown to the locals. Why else would the treasure still be there? Tutankhamun’s tomb survived almost untouched because it soon got covered by the backfill from a later, much grander tomb – which was robbed at an early date. And it certainly wasn’t possible for a few adventurers to wander into King Tut’s tomb guided by a map they bought from an old fellah at the coffee house. Carter had to employ a large team of farm workers to shift dirt for months opportunistically before they found the entrance.
Another possibility is that everyone around knows where the tomb is, but that it is tightly guarded, either by the authorities or by supernatural (possibly undead) beings. Since the treasure is still there, we may infer (again) that these guards make it too difficult for a few adventurers to wander into the tomb. You need an army. Archaeologists very occasionally do find treasures in unguarded tombs, and in every single case this comes as a surprise to us. Because if anyone had remembered the location of the treasure, they would have removed it a long time ago.
If instead there are sentient beings living in the dungeon, then to an archaeologist it is simply a settlement site, same in principle as the nearby farming hamlet I mentioned. Archaeologists don’t classify sentients into people and monsters, into good and evil. It isn’t clear to us upon arrival whether we can in better conscience raid the hamlet, the dungeon or more likely neither. We are simply dealing with paired settlements on either side of an ecological boundary. One practices agriculture and has few other riches, the other one does not produce much food but possesses great riches. Being so close to each other, the two communities must be aware of each other and in contact. We can see that any conflicts between them haven’t wiped either of them out so far, so most likely they are economically interdependent. The hamlet probably sells food to the dungeon inhabitants in exchange for treasure. Both communities are in all likelihood highly averse to the other getting wiped out by murder hobos. Such an equilibrium proves the farmers to be too weak to rob the dungeon dwellers and the dungeon dwellers unable or unwilling to farm the land. To an archaeologist, this setup is indistinguishable from a hamlet with a nearby stronghold or monastery.
If instead the dungeon’s inhabitants have only very recently settled there, it becomes difficult to explain why there is treasure in the dungeon. Did the new inhabitants bring it? Or did they defeat a group of strong tomb guardians? Either way, the dungeon is now basically an army encampment, and so again, not a place that four hobos can walk into.
There is also the issue of the underground spaces themselves. Most designers of D&D dungeons have a poor understanding of their physical characteristics. Are the underground passages largely natural caves? Then they will have quite a distinct morphology that differs depending on whether it’s a limestone karst system where a stream has eroded the rock away over millennia, a talus cave where fallen stone blocks have stacked on top of each other and left spaces under and between them, or lava tubes in a volcano. Such morphology is hardly ever recognisable on dungeon maps. Instead the spaces typically seem to have been excavated by means of mining technology, which demands enormous amounts of labour and produces spoil dumps nearby whose volume is about twice that of the dungeon or mine itself. Dungeon designers rarely pay much attention to the difference between natural rock sheets left standing in the dungeon, masonry walls and wooden walls.
Finally the issue of structural longevity. Archaeologists hardly ever encounter underground spaces that haven’t filled up with dirt or rubble. But there is often a sense in D&D that the dungeon is old. Since it is an open volume of air full of functioning doors and traps and hasn’t been flooded by groundwater, there must be magic at work unless someone is there to do continual upkeep and drainage work. And if, as seems to be the rule, the passages are artificial, then the integrity of the ceiling supports is of paramount importance. This is particularly true if the dungeon has been burrowed into earth or forms the basement of a masonry building. The basement of a ruinous castle quickly fills up with rubble unless masonry vaulting has been put in, and then the vaulting is likely groaning under the weight of rubble on the ground floor for which the structure was never engineered.
As you can see, studying archaeology is a pretty effective way to lose the ability to enjoy fantasy literature and roleplaying games not written and designed by archaeologists. But I believe that there are nevertheless pieces of archaeological information that can be used to add verisimilitude to your game scenarios, without making them hopelessly mundane.