The Wilderness

Adventure above the Dungeon
It is so much easier to understand White Box after almost 40 years experience with it. Of my original three Little Brown Books, vol. III The Underground & Wilderness Adventures shows the least wear. That is unfortunate because in many ways this is the volume that explains how to play the game. Vol. III details the underground or dungeon and the wilderness, which is about everything above the underground. On page 14 it is described:

The so-called Wilderness really consists of unexplored land, cities and castles, not
to mention the area immediately surrounding the castle (ruined or otherwise) which
housed the dungeons.

In order to take the game outside the dungeon, the referee must create a map of the area above and around the underground entrance. A town or village needs to be positioned nearby and a map drawn of it showing buildings and walls, if any, etc. The town or village then becomes a "home base" for the adventurers. And as vol. III suggests on page 15, "...players can have town adventures roaming around the bazaars, inns, taverns, shops, temples, and so on."
Vol. III suggests that "off-hand" wilderness adventures can be handled using Avalon Hill's Outdoor Survival map and gives useful suggestions for converting terrain on the published map into castles and villages. The authors note that journeys to find a legendary treasure or locate an area for planting a new castle should be handled differently, presumably by the referee drawing an area map and populating it appropriately.
Page 16 of vol. III gives specific guidance:

REFEREE’S MAP is a wilderness map unknown to the players. It should be for the territory around the dungeon location. When players venture into this area they should have a blank hexagon map, and as they move over each hex the referee will inform them as to what kind of terrain is in that hex. This form of exploring will eventually enable players to know the lay of the land in their immediate area and thus be able to select a site upon which to build their castles. (Castle building and its attendant requirements will be covered hereafter.) Exploratory adventures are likely to be the most exciting, and their incorporation into the campaign is most desirable. 

 Here we have an excellent description of the "hex-crawl" method of play and the end-game of castle building. For anyone with experience in wargames with miniature figures the idea that players would establish a strong hold or castle and begin to build an army of followers with which to "wargame" almost needs no explanation. It is with this "end game" in mind that vol. I page 6 refers to top level fighting men (Lords and above) building castles and becoming barons and clerics building castles and controlling territory similar to the "Barony" of fighters.
The securing of mercenaries and other hirelings, strongly implies role-playing. and regarding monsters taken into service, "Some reward must be offered to a monster in order to induce it into service" implies negotiation while players are in-character. I may be "implying" more than the authors originally intended, but it is the way I read the text these days.