Terrains are the areas outside of cities--the countryside, in other words. There are many different types of terrains, and each one has a unique appearance and its own NPCs as well as appropriate weather patterns.
Terrains, and the npcs in them, tend to be more similar between different types of terrain in the same general area as each other (for example, between plains and deciduous forest in the Ramtops) than between similarly-named types of terrain in different areas (for example, plains in the Sto Plains versus plains in the Ramtops).
Most terrains change a bit according to the season--having different appearances and room chats (with some npcs changing somewhat to match)--and, to a lesser extent, according to whether it's day or night, so the keen explorer will be rewarded for visiting the various areas at different times.
How terrains work
It's important to realize that terrains are much more continuous than cities, and that their scale is different. Each room is a square mile instead of being, well, room-sized (or at least, rooms are a mile apart), and you can generally go in any of the eight usual directions unless there's some sort of boundary there--even if it isn't listed as an obvious exit--because there's generally nothing to logically stop you from wandering in any direction.
The full ASCII map, too, has a different appearance in the terrains, reflecting their more continuous nature. In the daytime, in clear weather and with no obstacles, it's a circle extending ten rooms away from you in every direction, but--as in cities--things can restrict your view. Snow or sleet in particular contract the circle, and in certain types of terrain your view is blocked by natural obstacles: in forests you'll have difficulty seeing very far into the trees, and in mountainous regions it's difficult to see uphill. You also cannot see around cities. Bridges, on the other hand, are generally a bit higher than the surrounding terrain and will let you see over these types of obstacles (although, being higher, they can block your view the same way a city does).
Living things are represented with the @ character, and your own will be yellow (if you have colour enabled) and in the center of the map. As in cities, the full map will have a key indicating what the symbols mean--terrain types, roads, bridges, cities, etc.
In terrains you can move usually several rooms in one go--this is called journeying. For example, if you're on a road, the exits will normally be journey exits (although you can still take non-journey exits), and journeying will generally take you either eleven rooms (miles) along the room. The exception is if you journey into an intersection, or a room without another journey exit (bridges are walked onto normally, not journeyed through), in which case you'll stop there. This means that you don't generally need to worry about going past the turning you want.
If you're not on a road, you'll most usually go either six rooms in your chosen direction--and you can journey to the northeast, southeast, northwest, or southwest, even though these are not listed as options--or until you reach a room without a journey exit in the direction you're going, or a different short description (so, "An edge of plains near a stand of trees" is different from "Some plains"). You may not be able to journey in certain directions when near boundaries between types of terrains.
Whenever you journey more than one room, you're told the directions you went (well, skipped over, since you jump directly to your destination room without loading or interacting with the ones in-between).
Journeying is generally not an option in forests, jungles, mountainous regions, and water--only on roads and in more wide-open types of terrains.
You can opt to automatically journey instead of walking one room at a time (when the exit you're taking has that as an option) by setting "options personal travel" to "journey", and stop doing that by setting it back to "walk". (If it's set to walk, you have to specifically choose to journey a direction; just typing "north", etc., will only take you one room north.)
Finding your way
The latter part of the long description of a terrain room will give you a general idea of what major features (cities, roads, water, terrain types, and mountains) are nearby, and the approximate direction and distance.
If you have a physical in-game map for the area you're in and some adventuring.direction, you can also consult it, study it, or locate particular features on it to get an idea of where you are--though with low skills this idea can be somewhat inaccurate.
The Find ritual, if you have it, can also be helpful--npcs that can be flown to generally make good targets for the ritual, and will help you orient yourself in respect to a particular city or village.
The track command works differently in the terrains than in cities.
There are five broad (land-based) areas: Klatch, the Sto Plains, the Ramtops, Uberwald, and CWC (or the Counterweight Continent). However, Uberwald and CWC generally have the same sort of terrains as the Ramtops area (the main exception being the Uberwald forest).
There are also a few major bodies of water. The Circle Sea is just west of Ankh-Morpork and the Sto Plains. The Turnwise Ocean is to the northeast of the Ramtops, and the port city Bes Pelargic is at its edge. Thursday's Island is also in this ocean. The Widershins Ocean is directly to the east of the Ramtops/Uberwald area, and is basically southish of the Turnwise Ocean. A land bridge and glacial area divides the Widershins and Turnwise oceans. Finally the Agatean Sea is to the northeastish of the same land bridge.
Klatch borders the Circle Sea on its west side, as well as the Sto Plains. It extends north, west, and south to the borders of the map. Its most notable city is Djelibeybi, which is very close to the west side of the Circle Sea, although it also contains the Chronides Farmstead and Imtebos farmstead. It has the following terrains and areas:
- Water pastures along the Djel River, close to Djelibeybi.
- Farms around Djelibeybi and the Chronides Farmstead.
- Sandy beaches and rocky shores, which are of course next to the ocean.
- Extensive grassy plains and savanna throughout.
- The Ephebian Desert south of Djelibeybi and extending to the west. The Oasis is in this desert, roughly west-southwest of Djelibeybi.
- The Tsortean Desert north of Djelibeybi and extending to the west. The Klatchian Foreign Legion is in this desert, roughly northwest of Djelibeybi.
- Small stands of trees scattered throughout.
- A few jungles and rainforests
- A swamp beyond the Tsortean Desert.
The Sto Plains border the Circle Sea on its east side, as well as Klatch. They extend to the north to the border of the map, to the south to some mountains, and to the Ramtops region to the east. The most major cities here are Ankh-Morpork and, slightly to the east, Sto Lat, but there are several small villages and towns in the general area. It has the following terrains and areas:
- Plains, naturally, all around.
- Cabbage fields--miles and miles of cabbage fields--surrounding Ankh-Morpork and extending east to the Carrack Mountains.
- Rocky beaches, rocky shores, and cliffs which are of course next to the ocean.
- Small clumps of forest scattered throughout, and larger areas of forest to the west and south of Skund Forest, and in the far south.
- The Carrack Mountains, a mountain range approximately a hundred miles wide (from east to west) and around three hundred and sixty miles long (from north to south). Despite being "mountainous" terrain, the slopes are shallow enough not to require climbing.
- The Morpork Mountains, a mountain range starting to the southwest of Ankh-Morpork and extending some three hundred miles in a mostly southerly direction. Like the Carrack Mountains, no climbing is required here. The Capture the Flag arena is located on the east edge, at the end of a road, and Nowhere is located on the east side, at the end of a different road.
- Skund Forest starts around the south end of the Carrack Mountains and extends to the south.
- An unnamed hilly mountain range of the same type as the Morpork and Carrack Mountains lies to the far south, at the edge of the map.
Ramtops and Uberwald
The Ramtops and Uberwald area is to the east of the Sto Plains. It extends north and south to the borders of the map and east to the Widdershins Ocean. The areas of greatest interest are Lancre with its several towns and villages as well as Gloomy Forest, and Uberwald, a largish forested area to the far south of Lancre, reached by way of the King's Road and surrounded by mountains. The area largely consists of the Ramtops Mountains, although there are other terrains and areas there, mixed throughout:
- Deciduous forest, evergreen forest, and mixed forest
- Some marshland, which the road to the Sto Plains goes through
- Uberwald Forest ("Dark forest"), which is, of course, in Uberwald, and contains Escrow, Magpyr Castle, the Unnamed Town, and Dave's swamp.
- Moorland, with the largest area of it being to the east of the mountains, far past Uberwald. The Hublandish Barbarians' winter camp is here, near the inaccessible Fiddlyfjord.
- Rocky beaches and seashores along the Turnwise Ocean and inlets.
- Ice lands to the east of the mountains, leading into glacier and then the land bridge to the Counterweight Continent.
The Hub is also here, approximately nine hundred miles directly east from Lancre.
Past the glacial area is the Counterweight Continent. Most of the continent is inaccessible or nonexistent, but there are still several areas of land terrain outside the Wall. Bes Pelargic is here. Terrains include:
- Moorland on the land bridge
- Deciduous forest
- Seashores and sandy beaches along the edges of the land.
These terrains are much like their Ramtops equivalents, but the only human npcs on the continent are in Bes Pelargic and the Tuna Bay Fish temple.
- Unified terrains map of the entire playable Disc, compiled by Quow in 2018 for the Cow bar v3.6 "Explorer's Edition" update to the plugins, for complete mapping around the entire Disc.
- In other words: North, northeast, east, southeast, south, southwest, west, and northwest.