The World Born Dead
Explaining why there are dungeons
Alright, we know that you love dungeons. We love them too, despite the fact that we’re pretty sure there is no good reason for the silly things. The average D&D game world is frankly incapable of the technology or manpower needed to build vast underground complexes. I mean, look at our own world history: aside from a single underground city in Turkey and a couple of pyramids and tombs, the ancient world took a pass on underground life. Even the old excuse of “Wizards can magic it up and they do it because its defensible” is a bit lame considering that we are talking about a world with teleport and burrowing and ethereal travel; being underground is actually a liability since its harder to escape and people can drop the roof onto you, not to mention the incredible costs involved in doing it even if magic is available.
So here is what we suggest: dungeons have an actual magical purpose. By putting anything behind at least 40’ of solid, continuous material (like solid walls of dirt, stone, ice, or whatever, but not a forest of trees or rooms of furniture) the area is immune to unlimited-range or “longer than Long Range” spells like Scrying and transportation magic like teleport, greater teleport, the travel version of gate, and other effects. You can use these magics inside a dungeon, but you also stopped by a 40’ solid, continuous material in a Line of Effect; this means you can use these effects inside a dungeon to bypass doors and walls, but entering and leaving the dungeon is a problem, and parts of the dungeon that have more than 30’ of material in the way between your position and the target of your effect will be effectively isolated from your position.
In summary, in a best-case scenario you can transport yourself to a dungeon, then bust in the entrance and enter the dungeon, then transport yourself to the place you want to be inside the dungeon. In a worse-case scenario, the dungeon designer will have built the dungeon in such a way that only someone aware of the layout can take full advantage of unlimited range or transportation spells like teleports and Scry, or even that most or all areas if the dungeon are inaccessible to these effects.
Of course, there are exceptions. The idea of permanent portals, gates, or teleport circles are just too common in DnD and too fun to just abandon. Permanent effects will continue to regardless of materials in the way, and will be the premier way to enter and leave dungeons, as well as the best way to move inside a dungeon.
By incorporating these changes in your DnD world, you are ensuring that players actually explore rooms in your dungeons that you have painstakingly built, you avoid all the problems with Scry-and-Die tactics, and you’ll find that players actually care about dungeon geography. It also adds a bit to suspension of disbelief in your setting, which is only good for a cooperative storytelling game.