Every time you design something in your game, it should exist for a reason.
Now, that doesn’t mean that it has to have a grand purpose, but nothing should be there just because.
Let’s look at Dungeons and a number of reasons they should exist.
First, let’s define what I mean by Dungeon. I don’t mean a literal dungeon, I just mean any location that you have to travel through or into in a game that is self-contained and contains challenges, encounters, and goals. The goal can be as easy as “reach the other side of this forest”. Or it can be to retrieve something. Technically a city in your game can also be a dungeon if it contains enemies, challenges, and goals.
So here we go, reasons Dungeons can exist in your game:
1. It Moves Forward the Plot
This is the simplest one. By doing this dungeon, the plot goes forward. You fight a villain and stop them (or don’t stop them) from doing something dastardly, which opens up your next move. You find a MacGuffin in the deeps of the mountain that will help you stop a great disaster. Or just something like that.
Just to get to the other side, with no real development isn’t moving the plot forward. It’s just filler. But if every dungeon in a game only moves the plot forward, that might turn into a pretty short game. Now, not that there is anything wrong with that, but maybe we should have a few dungeons that exist for other reasons, what could they be?
2. It Helps Build/Develop a Character
Some Dungeons can exist to help flesh out one of your characters, without directly moving the plot forward. Maybe you discover the secret of their long lost brother there. Or it helps them overcome a flaw. Or the dungeon somehow challenges one of their flaws and you have to rescue them from their failure to overcome it.
All of these types of developments don’t necessarily move the main plot forward, but they can make your characters feel more real, more complete. Well developed characters are, in my opinion, the key to a successful game, so make sure you use this a bit, too.
3. It Helps Build a Sense of Scale
Sometimes things in your game just need to be far apart. And if you can travel almost instantaneously between them, it cheapens that feel of distance. And this is an ok reason to put in something in between! Just remember, you need to be doing it on PURPOSE, not doing it just to fill space. It isn’t about making the game longer, it is about communicating the length of the journey. It is about getting the right pacing for the plot.
There are many more reasons for a dungeon to exist in your game. Sometimes it is just because the challenge is interesting and engaging! Or maybe it is a mix of all of the above. You can be really efficient if you always make scale building dungeons also build a bit of character (my opinion, you should ALWAYS be building your characters), or even throw in a bit of main plot at the same time.
The main point is: Do what you are doing with a purpose and carry that into all parts of your design.