Not every trap in the world was placed there by nefarious forces bent on destroying the PC’s. (Well, since you as the GM place these, this isn’t technically true, but…) Natural types of disasters can fit this bill nicely.
Thick smoke hangs in the air, sting the eyes and lungs. In the distance, a wall of flame rapidly approaches.
Type: mechahical; Perception DC 5; Disable Device –
Trigger location; Reset None
A d100 * 5 foot wall of fire moves 1d10 * 5 feet per round in a single direction. Characters caught in the fire take 10d6 fire damage per round for 1d4+1 rounds, after which they will take 1d6 fire damage for 1d10 rounds.
This can be used in almost any setting where there is flammable material: grasslands, dry woods, or even high desert. If placed strategically, this trap can also make certain actions or encounters more exciting and create an interesting decision point. The characters may be heavily encumbered and on their way home from a nice haul, or perhaps there are only enough fire resistance potions for half of the party, and none for the horses.
It can also lend a sense of urgency to whatever the party is doing. Normally, deciphering some runes carved into a tree may not be exciting. The threat of incineration makes this activity a bit more exciting. The same would hold for a combat or NPC encounter, especially if the enemy is fire resistant.
These types of “traps” can be extended into whatever terrain your characters currently inhabit. Floods, avalanches, rock slides; these are all fair game in the wild outdoors.