Players will spend their time sticking their nose into other people’s business, mucking up plans, and generally being a nuisance to the established order. If you want this to truly be a sandbox, make sure their are plenty of places they could and would spend their time. Their choice to go hunt and kill a dragon will be made all more interesting if they are turning down a guild invitation, neglecting a cry for help from a small town, and marching past a lucrative dungeon. I try to create a whole bunch of half-baked ideas of what can be or is happening in the world around the players and sew them into the random encounters or the narrative of the things my players choose to pursue.
|A few hundred square miles is all they need to piss off a dragon, get embroiled in rebellion plots, attract the attention of an orc with a demon pact, and bankroll a new town.
Building a sandbox can be an incredible task and it often gets taken to mean that everything has to be built up from scratch. I have seen many games, including my own, fail as the dungeon master lacks the time to create everything and loses interest as their players do not see and appreciate every delicate detail the DM invested their time in. What I found helps is that I invest my time in making a skeleton: I draw a basic world map, name some power players in this world and region, I create a local hex map with some generic but interesting icons that can mean something specific or be left open to interpretation, and I write down a quick outline of “how this world works”. I will then add flesh to that skeleton as needed, starting radially out from where the players start and following where they travel and spend their time. I write down my plot ideas and nefarious dungeons, but start skeletal, adding meat as the ideas starts to see some interest from players, in the worst case I just reuse that content somewhere else, later. Above all, remember that this is a collaborative world. No one will remember the intricate plot intrigue that was planned, but the half-paranoid plot connections that the players made to account for the events in the game. The battle with custom monsters will be forgotten, but the shenanigans concocted to escape will not be. I try to have just enough ready off-stage so that my players can never tell what was just a random encounter and what I planned.
If anyone is interested, I can do a post about the program I use for mapping and how I use it.