Wilderness and dungeon levels

 Being able to assess the risk of adventure locations is a vitally important aspect of old school play, especially the sandbox style. In dungeons, this is a relatively simple matter: the danger increases as you descend deeper into the dungeon. Dungeon levels are typically numbered, starting with 1 for the first level, typically the most easily accessible, and progression to higher numbers with each level farther from the main entrance. Monsters found on a given level will tend to have the same number of Hit Dice as th e dungeon level (e.g. on the third level of the dungeon, 3 HD monsters are most common) and more loosely, traps and other hazards become more deadly. The amount and value of treasure also tends to increase with dungeon level. There are some twists on this formula; some dungeons may have additional entrances that lead directly to deeper levels, and some dungeons may be "layered" horizontally rather than vertically, but the overall principle is that players will be able to choose their desired level of danger and the corresponding rewards in treasure and XP.

On the other hand, wilderness exploration in older editions of D&D is pretty much a free-for-all. Some terrain types are a little more or less hazardous, in terms of encounter frequency and creature types, but there are no leveled encounter tables. In any given forested area, you could run into bandits, goblins, ogres, a cyclops, basilisks, or dragons, whether it's fifty miles from nowhere or a day's hike from the PCs' home town. The rules tend to hand-wave this with platitudes about how dangerous wilderness adventuring is compared to the dungeon -- even when that "wilderness" is near, or actually part of, an area inhabited by humans or demihumans. 

I'm sure it hasn't escaped anyone's notice that various video RPGs have dealt with this issue by making encounters more dangerous the farther the player's hero or party gets from the hometown. The first few titles in the Dragon Warrior series for NES exemplify this principle. Near the starting point at Tantegel Castle, the monsters are very weak; perfect for a green rookie hero just beginning his career. As you venture farther, you encounter stronger monsters. There were very few hard barriers between places, especially in the first game. You could theoretically walk from Tantegel Castle all the way to the big bad's fortress of Charlock as soon as you start a new game... if it weren't for the monsters getting tougher the farther from home you ventured. 

There's no reason why we can't adapt this principle to tabletop RPGs, despite the obvious differences. The campaign map can be divided into zones of danger, with progressively tougher encounter tables. First and foremost, these zones can be delineated by distance from civilized population centers. Start with Zone 0, which is a hex containing a village or larger population center. Zone 1 might extend three hexes outward from Zone 0. Zone 2 might encompass the next band of three hexes, and so on. We probably don't need to go much beyond Zone 4 or 5, except in special circumstances. Note that zones may contain creatures with a larger range of HD than a dungeon level. The emphasis should be on the threat posed by the creatures, so it wouldn't be unreasonable to have relatively docile animals with larger numbers of HD in low-danger zones, or exceptionally large numbers of 1 HD monsters in high-danger zones. 

It's not hard to come up with justifications for making this the standard order of things. Large settlements tend to have the manpower and resources to keep their environs safe for the population. Really big, scary monsters tend to be found in relatively small numbers, so despite their power, it's easier for the king's elite monster squads or bands of hired heroes to target them. Weaker but more numerous creatures, such as goblins, are much harder to ferret out and eradicate completely; they can hide in all the nooks and crannies even a fairly settled six-mile hex has to offer. As for smaller settlements, they're likely to be built, survive, and thrive in relatively quiet places. Nobody with any sense is going to try to build a new settlement right in the middle of giant-infested hill country (unless, perhaps, they have the support of a band of powerful high-level heroes who can either tame the giants or cleanse the area of them). And if powerful monsters do move into an area, villages are not likely to last long. 

To sum up, large settlements can maintain a low-danger zone around them, and small settlements will survive in low danger zones and die out if the danger level of their zone increases due to an influx of monsters. 

Within this general framework, there's still lots of room to play with things, and to make exceptions, without violating verisimilitude or player agency. Because settled areas tend to have low danger ratings, the existence or appearance of a greater threat is an anomaly. It's going to be something you've deliberately placed, not a random encounter on a table full of deadly creatures, and it's going to be talked about in-setting so the players will quickly learn of it and can adjust their actions accordingly. If you want to place a dragon's lair near the little village where your party of 1st-level adventurers begin their careers, the villagers will certainly warn them to stay away from it. In fact, it can be a source of inspiration and aspiration as the PCs can build their strength raiding goblin-holes and bandit hideouts until they feel ready to storm the dragon's mountaintop cave. 

Of course, Zones can be dynamic, changing quickly or slowly, and a campaign can make good use of that, too. Perhaps a town on the borderlands several days from the PCs starting point is threatened by a migration of tough monsters. They've thrown up a wall around their settlement, and have received a few troops from the capital to aid them, but the situation is not sustainable without much more serious intervention. The new monsters are roaming the countryside at will, so it's too dangerous for new PCs to tackle, but rumors of it will certainly reach their home, and they might make it their next goal to go to the aid of the other settlement, or just to tackle the bigger challenges in that region, once they've leveled up a bit.

Geographical barriers, such as mountain ranges and large rivers, can also serve to allow high-danger areas to exist in close proximity to low-danger areas in a stable situation. The tougher monsters in the high-danger zone find it difficult enough to cross the barrier that they do not often trouble the low-danger zone, but adventurers may find it worthwhile to make the trek through a treacherous pass or take a boat across the river to explore the high-danger zone.

Finally, you can create very high danger zones, beyond what naturally exists in the campaign. For instance, the lands around the castle of an ancient lich or a portal to the Sphere of Entropy might be crawling with insanely powerful creatures. Naturally, these zones should be visited only by very high-level parties. The creatures of the zone may be contained by natural barriers such as impassable mountains, magical forces, or simply whatever arch-fiend controls the area doesn't want them to go forth and conquer at the present time.

Now that we have that squared away, let's talk about dungeon levels. Mid- and high-level characters can still dungeon-crawl, but the first few levels of a traditional dungeon are of very little interest to them. The players of such a party are going to be bored with the first few dungeon levels, and you as DM probably don't want to have to map and stock them, either. One way of mitigating this is as mentioned above, lesser-known entrances that go directly to deeper levels. Another way is to start the dungeon at one level harder than the surrounding wilderness zone is. If the dungeon is located in Zone 3, then the entry level of the dungeon is Level 4.

Of course, it's important to telegraph difficulty levels to players so they may make informed decisions. This is especially true when you place monster populations or dungeons that don't correspond to the standard order of progression. You absolutely may place a red dragon's hilltop lair, a camp containing 100 orcs, or a dungeon with an entry level of 5 in a Zone 0 or 1, so long as you communicate to the players via NPCs, books, or other sources of information that it's an especially deadly place.