As those of you who follow me on Twitter might know, I wrote up a dungeon for OD&D to run at this year's D&D Experience. Unfortunately, I didn't get the chance to run it at the con. However, I learned a useful lesson going forward: From now on, when I design an adventure I'll first approach it as if I'm running it using OD&D.
This approach might seem a little weird, but it makes a lot of sense when you think about it. OD&D keeps characters simple. They don't have loads of spells, abilities, or magic items. The monsters are built in a similar way. An orc swings its sword or fires its bow at you, and that's about it. Critters like beholders and dragons are a little more complex, but they're the exception, not the norm. There are no skills to roll, just descriptions of what a character tries to do.
When you pull those things back, you're left with only one option for making a dungeon or adventure interesting: Compelling locations, mysteries, puzzles, weird phenomena, *stuff* that the PCs can poke, prod, and inspect. These are all the things that make D&D compelling. They show off the spontaneity, immersion, and creativity that arise in the exchange among players and DM.
In Search of the Unknown is a great example of this effect in action. The dungeon in that adventure is empty of monsters and treasure. The DM is supposed to add that stuff. Instead, it features an overgrown garden of massive mushrooms, a chamber of mysterious pools, hidden chambers, details and color that suggest the dungeon's history, and other elements that make it an interesting place to explore. Reading the adventure, even without monsters and treasures, is fun. You want to know what's in the next room.
That's what this approach embraces, creating a dungeon environment that's interesting without any monsters around. It builds an environment that encourages the players to think of the scene from their character's point of view and act appropriately. It adds enough detail to get things started, and relies on the players choices, rather than the mechanics of skill checks or powers, to drive the action.
Once you have those details nailed down, you can then go back and add in monsters, treasure, skill DCs, and what not as appropriate. If you are running 4e, this approach has probably already yielded some interesting dungeon features that the monsters (and the PCs) can use when a fight breaks out, but you should also have plenty of areas for exploration and experimentation, nice changes of pace from the funhouse effect of one fight after another.