Realism should inspire, but not dictate dungeon design.
In my opinion, the worst issues that a lot of RPG dungeons suffer from are:
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Symmetry. The designers do a lazy copy paste by mirroring the layout from left to right. While it is true that a lot of real world locations use symmetry, it does not make for exciting dungeons. It means that to the players there's no real difference between turning left or right at that central intersection. It all looks the same.
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Flat dungeons. Just because we tend to draw our maps from a topside view, does not mean that the dungeon itself needs to be flat. Dungeons are far more interesting when they make use of height differences, staircases, balconies and bridges. Consider for example that a large church hall could have an upper level. Depending on the dungeon, you may even want to challenge yourself and try a sideview for a change. Many designers don't include rooms that overlook other rooms in their designs, because it is easier to fill a sheet of graph paper by putting the rooms side by side. But in the real world, our buildings have plenty of rooms with multiple levels. Such rooms are also far more exciting in relation to ranged combat.
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Long corridors and empty rooms. The goal of a dungeon should not be to fill the edges of the paper. Adding pointless rooms is easy. But removing stuff is hard and often better. Trim the useless filler and reduce your dungeons to actual content. Fill your dungeons with meaningful content and leave out the rest.
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Purpose is not kept in mind. What are all these rooms for anyway? And what is in them? What function do they serve? If your dungeon is a temple, where do the priests go to pray? Where do they sleep? Where do they eat? Dungeons are so much better when purpose guides some (but not all) of the design.
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Linear progression through the dungeon. A big mistake that a lot of designers make, is having a lot of linear corridors with dead ends. Ideally a dungeon contains a lot of choices and hallways that connect back to earlier parts of the dungeon. In other words, there should be more than one viable route through the dungeon. Dead ends are also content that the players can easily skip, often unintentionally. It helps if there is more than one way to get to those areas of the map.
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Square room syndrome. It is easy when drawing out a dungeon on graph paper, to make every room rectangular. But it also makes for a very boring lay out.
View attachment 117706
Unsurprisingly,
@Oofta 's example of a bad dungeon shows nearly all of these shameful traits.
Highlighted in red, we see the symmetry issue. Some symmetry is fine, but the central mirrored room is an eyesore. Highlighted in blue we see long empty corridors. These corridors often seem deliberately as long as possible, even when shorter routes were available, such as with the corridor to room 34, or the tunnel connecting room 18 and 21. Highlighted in green we see dead ends. Not all dead ends are bad, but they shouldn't dominate the design. Dead ends mean a lot of backtracking, and a lot of content that the players could skip accidentally. To improve the flow of the dungeon, any of the green areas could be connected to other parts of the dungeon. Also, most of you will have noticed that nearly all rooms in this dungeon are rectangles and there are no rooms overlooking other rooms.
Now, I'm judging this based on just the picture alone. I did not take into account any secret tunnels that may exist in the design but may not been clear from just looking at this map. I'm also not taking into account deliberate design decisions. But my rules are not absolute. If you feel that ignoring one of these rules the right thing to do, then by all means ignore what I said and do what feels right to you. There is no taboo on dead ends or long empty corridors just because I said so. Just beware that you don't overdo it, and take these things to heart when designing a dungeon.
Edit: I had a look at the Caves of Chaos map from Keep on the Borderlands... and oh dear, it is like looking at Oofta's example map, but ten times worse.
Imagine how much better this map would be if they removed half the rooms, and stacked half of what was left on top of the rest as a different floor. I was honestly surprised that they wrote "
slope" at the top of the map near room 38. As if the designer realised very late just how flat the map looks. You also got to appreciate how they sanded the edge off the corridor (g) above room 20. It is like the absolute minimal effort you could possibly make to have the dungeon seem slightly less rectangular.