A tabletop role-playing game always plays on two levels at once: The story level where the warrior chops off the head of the orc, and the game level, where a player rolls some dice. The art of Dungeon-mastering is to balance these two levels and to connect them. By treating travel and survival in the Underdark as a series of dice rolls, with modifiers based on player decisions, the players gain agency over the story. And unexpected dice rolls can add surprise to the story. The Out of the Abyss book, chapter 2, has some very good suggestions on how to handle travel and survival. I just needed to combine that with existing rules in the Player’s Handbook and Dungeon Master’s Guide to a “loop” of rolls to do every day: A roll for navigation in order to avoid becoming lost, a random encounter roll for during the day, another random encounter roll for camp at night, and a roll for foraging.
The trick to make all of that a bit more interesting is the drow pursuit: Players can choose to travel slow, normal speed, or fast. Traveling fast makes them gain more distance from the pursuers, but prevents them from foraging, and increases the difficulty of navigation and perceiving enemies. Traveling slower increases the risk from the pursuit, but makes everything else easier. In this session we played through that loop for 7 game days, which with several days traveled at high speed meant the group went from the drow outpost Velkynvelve to the kuo-toa village of Sloobludop.
To give the group some means of orientation I used the previous encounter of the cleric with Juiblex to give him a level 1 madness which made his face wounds burn whenever he looked in the north-western direction from Velkynvelve (towards Blingdenstone to be exact, for reasons that will become obvious much later). That gave him advantage on navigation rolls, and the group used a second character to help with navigation when they were traveling at fast speed, so they never got lost. After the first day the cleric also switched spells to have Create Water, which solved their thirst problem.
As encounters we first had one attack at night by goblins, which weren’t too hard to beat and provided the ranger of the group with a short bow and arrows. It also turned out that the players weren’t the squeamish kind, and they filleted the goblins, cooked them over magical fire, cast Purify Food & Drink on the meat and ate it. Later in the session they encountered a bunch of gnolls, which are larger than goblins, and thus ended up with more than enough food for their journey (although I ruled that meat wouldn’t keep longer than 2 days, because otherwise the whole foraging thing would become useless).
Then they came to the Silken Paths, an area of spider webs crossing a large chasm, connecting stalagmites and stalactites. Two non-aggressive goblins had created a business guiding people across, and the group agreed to pay them for passage. On the web they found a large chest, which of course turned out to be a mimic (that still works with new players). Then they were attacked by darkmantles, which after killing them they used to make waterskins out of. In fact this group is the first one I see in 5th edition which makes use of crafting skills from their background. Once over the chasm, the group decreased their pursuit level by burning the webs they had crossed, although of course they couldn’t burn the whole giant web.
The gnolls they met in an encounter which was supposed to have them come upon a hunt, with the gnolls chasing a pair of hook horrors. But the group just cast a fog spell to hide from the monsters and then traveled on. Then they came upon the second half of the hunters, and killed them. The group decided to rest there, but of course the first group of hunters came back before they were rested and they had to fight gnolls again.
At the end of the session the group arrived near Sloobludop, and gained level 4 from the xp for survival and the various encounters. Just like in other campaign books of Wizards of the Coast, level increase is at least twice as fast as what you’d get if you just gave out xp for monsters. I decided that was okay, as nobody wants to be low level for too long. I might have to slow that down a bit if I feel that the group is becoming too powerful for a dark themed adventure.