I discussion of megadungeons vs small dungeons on the RPGsite reminded me of how I handled dungeons in one campaign in the late 1970s. There was only one real dungeon in the world, all dungeons deserving of the name were magically linked. Not obviously linked in many cases, but linked nevertheless. In some cases magically linked corridors were only open to monsters or people who were initiates of particular chaotic deities. Others were only connected by hidden teleportals or even gates that only opened at certain times, in the presence of certain items, or even only when certain rituals were performed.
Dungeons usually did not start out linked as part of the megadungeon. However, when a dungeon, a cave system or even goblinoid tunnels grew beyond a certain size, a link or links to some part of the megadungeon would appear — sooner or later. Some were other these links were created on purpose by wizards or powerful magic-using monsters, but others just seemed to appear. A knowledgeable (and powerful) character, NPC, or monster could take advantage of these interconnections to travel the world relatively quickly (and without using traceable magic like long distance teleports or opening a gate), provided he or she (or it) did not mind a dangerous journey through dungeons to get there. Intelligent monsters used this method of moving around a lot. One powerful lich even managed to run four separate small kingdoms without anyone being aware that each kingdom was ruled by the same being as his home sat over a small part of the megadungeon that was somewhat of a nexus between many other parts of the megadungeon.
These connections even extended to a few alternative versions of the prime material plane. One connection the players found opened to the dungeon beneath the city of Jakalla in Tekumel. Another corridor opened into a corridor on the USS Enterprise, a corridor that only those with the ability to see magic could find from the “Star Trek” side. Although no PCs ever went deep enough into dungeon(s) to find it, the very lowest levels connected directly to the Abyss.
The connections to the Abyss, of course, were the true source of the ever expanding connections that incorporated dungeon after dungeon into the megadungeon. The powerful demons and godlings in the Abyss had a plan to incorporate the prime material plane(s) into the Abyss by creating many connections between the Abyss and the prime material plane(s). Eventually, they would send billions of demons and other chaotic creatures through these connections and conquer the prime material plane(s). Of course, being highly chaotic and unwilling to work closely together, the invasion never happened. Actually invading would require far more coordination and cooperation than chaos could muster. But the megadungeon just kept growing and expanding….
Are the dungeons in my current Microlite74 Wilderlands campaign linked in a similar manner? That would be telling.