I've found that almost any combat encounter in 4th Edition Dungeons and Dragons
requires interesting terrain to be effective. The core rulebooks do a good job emphasizing how terrain affects movement and the overall flow of a fight.
Unfortunately, Wizards of the Coast, the publishers of D&D, sometimes break their own rules. I thought it might be interesting to compare and contrast the DMG tips on terrain (which are really quite good) a dungeon in a published 4E adventure - Thunderspire Labyrinth's "Horned Hold."DMG Rule #1 - Bigger is better
A typical 4E fight involves 5 PCs versus about 5 monsters, all of which occupy their own distinct squares on a battlefield. The DMG is pretty explicit here: cramming everyone into a 10 foot corridor usually makes for boring gameplay, since it's hard for the party to flank enemies and vice versa.
Here's a rule of thumb that I use - multiply the number of actors in a particular fight by ten squares, and use that as a minimum space for the fight. So for my "Sparks of Fate" campaign, which features just 3 PCs, most of the combat areas are at least 60 squares large ((3 PCs + 3 monsters) x 10).
Does the Horned Hold dungeon comply with this design precept? Well, the "boss" encounters with the Duergar overlords are done pretty well; you usually get large open rooms to work with. Some of the smaller encounters take place in very small spaces (the initial tussle with orc berserkers is a good example) unless you let fights go from room to room. Which brings us to the next rule...DMG Rule #2 - Use cover and difficult terrain
As a practical matter, most rooms and caverns aren't empty. In terms of gameplay, it's always better to have detritus around the battlefield that forces people to make tactical decisions. And dramatically, a combat scene is just more memorable if there are things to interact with (the teahouse shootout in John Woo's "Hard Boiled" is a really good example).
I tend to do things holistically; I imagine where the encounter is likely to take place, and try to design neat terrain around that concept, rather than shoehorning flavor onto a preexisting battle map. For "Sparks of Fate," I knew one crucial fight would occur in a warehouse (a typical D&D setting if there ever was one), so I based the warehouse on the final scene in "Raiders of the Lost Ark." That meant big crates, catwalks, metal braziers that acrobatic characters could swing from...all fun stuff that made it into the final product (and the fourth Indiana Jones movie, BTW).
This is probably where Horned Hold needs the least improvement. Of course, the whole design is based off of the "fortress" archetype, which is pretty much a license for any kind of architecture. Still, there are large stone bridges, a decrepit chapel filled with rubble (and wights), and some neat slave pits, so it's not totally blank. Even in the more mundane rooms (barracks, storerooms) there are tables and beds that can be used in creative ways.DMG Rule #3 - Think in three dimensions
If war has taught man anything, it's that whoever holds the high ground has a big advantage in combat. D&D, for game balance's sake, doesn't give the elevated attacker excessive benefits, but elevation still serves some important roles in terrain design.
Elevated positions allow ranged attackers line of sight while impeding most melee attackers. Unlike typical difficult terrain, though, an elevated position has a certain movement flow - it's faster to jump down from a ten foot dais than it is to clamber on top of one. This can make for an interesting decision when a monster drops a poison gas cloud on the ridge the PCs are attacking from - do they stay and take damage, or jump down and lose the benefit of being isolated from melee monsters?
This is an area where Horned Hold really falls down (no pun intended). The whole dungeon, as far as I can tell, is flat as a pancake. Even some stairs or balconies would have livened things up. It's just not the most exciting structure to fight in.DMG Rule #4 - Make terrain flavorful
The DMG actually urges you to make terrain "fantastic," but I think what they're getting at is to pile on layers of detail so that a combat encounter comes alive. A fight on two wooden platforms is usually not as good as a fight on two rickety rafts careening down a river in the middle of the jungle.
Another tip that belongs here is to make sure that the fight is linked, somehow, to the arena itself. This adds urgency and realism to most fights; after all, if the monsters weren't all around the King's unconscious body, there'd be no reason to stick around the throne room to fight them. One of my friends created a fight centered around a huge, elaborate ritual, along with the mechanism that was used in the villain's plan. You couldn't just abandon the place, though, since you wanted to stop whatever it was that was happening. It's a classic trick, but a good one.
Horned Hold does an okay job here, with the fight in the blacksmith's forge making the most sense. A lot of the other fights seem to be optional; the PCs can simply elect to avoid or run from those encounters, and there's no plot weight tied to them. I know some DMs prefer this style, but I like to drive the story ever forward with each fight.Final Thoughts
I think that above all, terrain should be understandable by the players. Instead of drawing symbols that indicate rubble, go ahead and draw out rubble. Instead of trying to explain what something is, just label it on your map in big print (a good marker and an eraseable battle map are almost required for running 4E). And if something sounds like it might be plausible in a fantasy novel - ripping a door off its hinges for mobile cover, freezing a chandelier chain and then breaking it apart with an arrow - I like to let players do it. In the end, most pen and paper roleplaying games are collaborative, and 4E D&D terrain should be part of that act.