Sure you have caves and dungeons nearest, you have a bit of dark wilderness to explore. But you also have, in a ring a little farther out from the starting location:
- a village that needs defending à la Seven Samurai
- a heavily protected but legally accessible site, like a temple or shrine, that players might want to heist something from
- a town just large enough to allow for hunter/hunted type scenarios
- an infamous prison/enemy camp players might need to make a prison break from if captured
So the things each of these kinds of adventure need would be subtly cooked into the setting. If players want to engage those sandbox toys, they can and the DM will be helped by them existing already. The DM would also be given what would help with each kind of adventure. So, the temple would be mapped with guard patterns and schedules and a friction point type escalation plan. The village would have a tactical scale map and a bit about the attackers' goals, strategies and time table. The hunter/hunted would have a layout of leads and escalating reprisals by the hunted. And maybe it wouldn't need to be in a town, it could be a secret society or evil type that spans the whole map. The prison could also function as a place to perform heist-like rescues, having it perform double duties.
What other types of adventure would you want to provide for in a basic, all-purpose, but classic campaign?
- Maybe a hopping tower that would be good for solo adventures. It travels around so it can be wherever the player happens to be, it's smaller and contained so one player won't be overwhelmed, it's rare so it's something cool the one player that came get's to brag about experiencing it to the other players.
- The tiniest bit of sea to allow for sea adventures, maybe a fishing village right on the edge of the map.
- an un-activated, magical portal of some type as a wild card.