Dungeons are a thing of beauty, but too often I see empty, endless looping corridors where nothing ever happens save for the occasional wandering monster. Mazes are awesome, options are great, but what is beautiful, isn't always playable.
Take Map A above. All good right? Nothing you haven't seen before. But unless something happens in those passageways, you're going to waste a lot of time slogging from room 1 to 2 (especially if someone's mapping.) It might look cool, might be fun to draw, might look fun to play, but it kind of isn't. You could just do this.....
Map B might seem dull, but it's gonna make your session run a lot smoother. You just saved about 20 minutes of unnecessary slog. But that's no fun. You want that dungeon to be a labyrinth. You want that sense of exploration. You want those players cautiously peeking around every corner. You want them interested in the entire place.....not just the rooms. Too often, hallways are just time-killers.
They shouldn't be.
Almost every time the players turn a corner something interesting should happen. This doesn't have to be a fight, just something interesting. Dungeons should not only be places of danger, but places of wonder.
Now look at Map C below. I've added a fountain, a one-way door, an alter, a statue, a portcullis, a curtain, some stairs, and a huge pile of rubble -- all outside of rooms. Not everything will be dangerous or meaningful, but the players sure as hell don't know that. Every turn of a corner becomes interesting now.
Many of these objects should do something. There should be a trick, something hidden, a treasure, a trap, a penalty, or a perk. At a minimum on Map C, the players will have 2 encounters while traveling between the two rooms. These encounters can make sense or not make sense, but most of them should adhere to the theme of the dungeon.
And that's all it takes to liven up the place. Now that small, 2-room section of dungeon is packed full of goodness.