Tried to get involved with a thread on Enworld but it appears the participants want to beat the hell out of each other rather than have a discussion.
Anyway I wrote down some observations on sandbox campaigns that I think the rest of you may find useful.
After Necromancer Games released the Wilderlands of High Fantasy boxed set was released the various authors, including myself, began to explain what the product was, and how they used it. Sandbox campaigning turned out to be the best term to package up what we were talking about and it stuck. No idea who came up with it specifically.
My own particular interest in the sandbox campaigns is developing the numbered hex map pioneered by Judges Guild and used in the Wilderlands Boxed Set. I feel it is a compact way of presenting a setting that is ready to run out of the box. Part of the reason behind my two Points of Light was to give an affordable example of format that didn’t involve shelling out $70 (the price of the boxed set).
Pieces of advice to anybody wanting to run a sandbox campaign are
1) Things don’t happen in a background, unless there a special reason people for miles around are going to know there is a dragon lair on Grimbolt Mountain. They may not know exactly where it is but the fact there a dragon in the general area is going to be obvious. This the same for a variety of locales with dangerous creatures. Most however will have to be discovered by the PCs actively looking for rumors.
2) Plot can occur in a sandbox campaign and it is best implemented as a series of events written as if PCs didn’t exist. Consider this as a plan that will change once the PC get involved. They also may not want to be involved so plan for that.
3) The most effective use of a sandbox campaign comes when the character have a background that ties them into a region, culture, religion, or organization. This gives the player a context in which to start making decisions about what direction they want to pursue. I find this works best when limited to a page and developed from a private session between the referee and players talking back and forth.
4)Detail is important but you will never have enough time or interest. The technique to overcome is to develop of a bag of "bits". Bits are situations, locales, npcs, props, etc with the serial number filed off. They can be combined in different ways to provide on the spot locales and encounters. You can fine tune the exact mix in order to impart a specific feel to the setting. Much of my bag of "bits" revolve the medieval theme which lends my campaign a more gritty and serious feel. Your may be different.