It should be apparent to anyone that's read my blog for any amount of time that I prefer sandbox settings. My favorite module for any system is GW1 The Legion of Gold that outlines the Barony of Horn for Gamma World followed closely by B2: Keep on the Borderlands that outlines the surroundings of the Caves of Chaos. And, of course, who can forget T1 The Village of Hommlet? Adventures that have add-ons, such as the wilderness areas for Rappan Athuk or Freya's Crucible (both originally by Necromancer Games coincidentally; RA was recently upgraded to Swords & Wizardry and Pathfinder editions by Frog God Games, the successors to NG) fall into the sandbox category to some extent as well. The focus of these modules is, of course, on the megadungeon or the plotline respectively, but sandbox material is provided as well. While I've stated in the past that Greyhawk is my favorite campaign setting, the Wilderlands/City State of the Invincible Overlord by Bob Bledsaw and the Judges Guild runs a very close second. The setting is very sandbox and gives sparse details on the campaign maps for the DM (Judge?) to develop.
The best thing about sandbox adventures is that it's a lot like a buffet. The DM sets out the food, and the players choose what they want. Admittedly, it is a lot of work for the DM, and he can't be a control freak. The players just might take their characters completely off-script. Now, occasionally, the DM will have had a busy and no time to think, much less plan for a game. The players might want to head off for Greyhawk City when the DM has only prepared adventure hooks (weeks before) around Hommlet (where the players are). In a case like this, there's nothing wrong with telling the players, "Guys, I've had a week from Hell. I know you really want to go to Greyhawk, but I'm not prepared at all for that. Could you go after a hook in town? I'll work up plans for Greyhawk City for next week." Most players will understand and go with it; we've all had those weeks.
The ability to improvise is a key skill as well. Maybe the DM is good enough to roll with the journey to Greyhawk and can come up with something on the fly that fulfills the players's expectations. If one can do that, great! Go for it. If the players feel like their choices and input influence the game, they become invested and interested in the setting and will want more! If they don't have that feeling and instead feel like they're on the Plot Wagon (TM), well, they may as well be playing EverQuest 2. Or, worse yet, WoW.
Another ability to keep in mind is recycling and I'm not talking about newspapers and aluminum cans, either. In this instance, it refers to using adventures that the players have bypassed; this is not railroading, either, but a labor-saving device. Let's assume that in the Hommlet setting mentioned above, the Judge had worked up a goblin warren to the southeast of Hommlet; however, the players have elected to take that journey to Greyhawk. On the journey overland, Fate intervenes and a wandering monster check indicates an attack by goblins. Rather than just randomly rolling the goblins up, the party is attacked by a patrol or raiding party from a goblin warren. The players decide to follow fleeing survivors and find the lair. Recycling in action. And note that this goblin warren is not in the same location; this could be three weeks out on the way to Greyhawk. It has been transplanted, and the DM has a week to work on Greyhawk! Also, be careful not to MAKE the players go where you want. If the players killed the goblin patrol or let the fleeing survivors go and don't look for the lair, so be it. But you were ready if they did!
Another good example of this is reusing vintage modules. When I first started the Guardians of the Polar Bear (my God, was that 2004 when Kat was nine and Rene' was seven?!!), I placed the Necromancer's mansion from U1 The Sinister Secret of Saltmarsh on a rock atoll about a mile-and-a-half on the road north out of Hommlet. The caves at the bottom opened into a forest clearing. The necromancer had disappeared about the time of the Battle of Emirdy Meadows. The pirates became a detached group of bandits and gnolls from Lareth's moathouse and thus tied into the overall setting in a different way than before. Recycling; learn it well.
Finally, the sandbox DM should learn to use communication with his players. Help them determine a real background for their characters. Ask for their input after a game; see what goals that have and what they plan to accomplish. One can see this in the Hommlet campaign with the NPCs. Elmo mentions his brother Otis long before the players ever go to Nulb. A PC's family can be the source of new characters if the original character falls in battle, such as poor Kane Deathchant. Maybe the character is the young scion of an Elvan noble family from Celene. Upon reaching 4th level, news of the character's exploits have reached Celene and the character's family (or maybe even Queen Yolande herself!) sends the character a gift in the way of a Quiver of Ehlonna with 6 +1 arrows. Deus ex machina? Maybe a little; but it does help the characters in game and also helps keep them invested in the story.
Overall, sandbox settings are a lot of work to set up. However, properly executed, they can create a world that feels as vibrant and alive as anything in the works of fiction and definitely better than a static MMO.
Until tomorrow, gentle readers, dream of glory and adventure!