Mapping a cave that the players will probably never return to again is not something I'm interested in. I do however want the cave itself to be an obstacle, because you know, caves aren't exactly a walk in the park. Depending on the size you could easily get lost for days, weeks, or months and die because you only have rations and water for a few days.
So it's important to have a party member who knows what the fuck they're doing.
We'll call that party member the scout. Whatever party member has the "survival" type knowledge. If no one in the party knows how to track something, or read a map, or tell which direction they're marching– dont look now, you might be fucked.
When the party gets to the cave, or swamp, or whatever thing you dont want to map. The scout rolls a d20 and adds either their wisdom mod or whatever number they have that is relevant to leading the party through the wilderness. Depending on the size of the place, roll 3(sm), 5(m), or 8(lrg) times.
1-8. The scout leads the party into danger. Roll up an encounter and expend some resources, shit just got real.
9-11. You are walking in circles. Expend some resources.
12-17. Hurray! You seem to be on track, and nothing of note happens.
18-20+. Wow this scout kicks ass, they not only found a good route, but also some tasty mushrooms, fresh water, or maybe even an old stash or gear from previous adventurers.
Having a map (in game) of the area will get you a +2 to the check, and knowing how to read maps will get you a +3.
If the scout has been through the cave before, they may make a roll under wisdom check to see if they remember it correctly. If they do, they need only roll once, no matter how large the place.
Use in conjunction with this excellent wandering monster procedure from the Retired Adventurer.