First, you as a DM will need to make a visual or mental map. Then, I need to decide on the following: How long is each route? How dangerous is each route (or each section)? How easy is each route to navigate (or each section)? And how likely is the party to get sidetracked by an interesting discovery on each route?
Danger is measured from 1 to 5.
- 1 is a relatively safe, civilized region or a barren, desolate region.
- 2 is a dangerous frontier.
- 3 is enemy territory.
- 4 is regularly patrolled, extremely hostile territory.
- And 5 is reserved for the sort of terrain which is filled with monsters that are actively trying to destroy all intruders and can detect the intruders with supernatural means. For example, Hell or The Land of the Dead. Seriously, 4 and 5 are pretty ridiculously dangerous. You’ll see why.
Navigation and Resources are both measured in terms of a DC. But either can be moot. For example, following a road or river makes Navigation moot. And traveling through civilized, friendly farmland makes Resources moot. Otherwise, you want to set a DC of 5, 10, 15, 20, 25, etc. in D&D 5E.
- Gently rolling flatlands have a Navigation DC of 5 or 10.
- A Desert has a Navigation DC of 25 or 30. If you want to add a Fantasy Factor like confounding fair curses or the blessings of the Land Spirits, you can adjust the DCs by 5 either way.
The players need to have a choice in what route they will take on the journey. The routes should be in conflict, e.g. longer and safer or shorter and more dangerous. They should have a decent understanding of the choice (distance, time, difficulty). Set travel pace for the day; slow, normal or fast.
- Slow = Advantage on Perception and Survival checks. Chance to surprise enemies. 2/3 distance covered. Enemies have Disadvantage to detect.
- Normal = Nothing.
- Fast = Disadvantage on Perception and Survival checks. Risk of being surprised. Enemies have advantage to detect.
Take 6 * d6. Each one represents a time-period of the day. Morning, Afternoon, Evening, Dusk, Midnight, Predawn. Roll them all. For each one that shows the Danger number or less, an encounter MIGHT happen. We’ll talk about random encounters. For example, if the Danger is 3, and your six dice show 5, 2, 3, 4, 1, 6; the party will have three encounters that day. One in the Afternoon, one in the Evening, and one at Midnight. Notice that the danger number is actually the number of encounters you will expect to happen in one day.
Finally, roll one more d6. If that shows the Discovery number or less, you need to tantalize the party with something interesting off the road for them to check out. A ruined tower, a sign of magic, an old tomb, an ancient henge, a shrine, or whatever. The key is that it has to be far enough off the path that the party has to choose whether to waste a few hours investigating it or to ignore it.
Now, play out each daytime encounter as they happen. The party might rest etc. between. Remember that surprise is possible, the pace plays a big role here. Encounters can be circumvented or missed.
Make camp. First we need to figure out if the group is lost. Have someone roll a Survival check against the Navigation DC. Make this a hidden DM roll. Secondly, how far did the party travel? 2/3, 1 or 1 1/3. If they stopped to investigate a discovery, subtract 1/3.
Now, play out nighttime encounters. Roll randomly who is taking the watch unless the party is very determined in deciding. Wake up, start over.
Lost If they get lost, log no progress in distance. Have the navigator roll a Survival check to see if they realise they are lost. They get the info on the morning. Each day that they travel while lost, roll a d6 when logging their progress. On a 1, they managed to travel in the right direction and log progress normally. On a 5 or 6, they are losing ground and subtract however much progress they would have made based on their route. For anything else, add no progress. If they figure out they are lost, they need a new plan.