Whilst exploring underground the PCs discover tube like tunnels stretching for miles, upon further inspection the strange tunnels seem to connect all major cities in the are, what is their purpose?
A nifty little encounter appropriate for any powerful sorcerer/magically adept monsters lair.
When the party have penetrated to an appropriatly impressive level/room they encounter The Door, this door is a vessel through which the Sorcerer/Monster can safely work against any intruders, the door is heavy duty iron bound studded oak wrought with craft skill and magic, set in the middle is a crystal orb, once the party get within a preset distance the orb flickers briefly as the door warns its "master" of the intruders, the master can then effectivly possess the door itself, this means that all movement the door is capable of (i.e. opening and closing) come under the control of the master, the master can also cast spells from the door as if he were there himself, all the while any damage that is inflicted in return merely damages the door, this will in effect ruin any of the parties chances of surprise, allow the master to assess the parties abilities while remaining safe and sound and finally will probably cause the party to waste some of their juicier items/spells on a chunk of wood and iron, and if the master happens to have a deadly spell or three it could also reduce the size of the party,
Of course if you wanted to be really nasty you could have the door open to admit one person and then slam shut on the second person (squish) whilst blasting away with every spell in the mastrs repetoir
The PCs discover a large white ball in the branches of a tree, or in a niche in a cave. Unless magically examined, or by a PC with a specialty in insects, it is a plain, smooth white ball. After a short time, it hatches and releases hundreds of spiders, cockroaches, some other nasty bug
A corpse lays at the side of the road, or path. The man has been robbed of everything but a few tattered pieces of clothing. It looks like the scavengers have been working on him for a few days. The smell is ghastly. What dangers lay ahead?
On a location with numerous webs, and at least one big spider, there is a something inside a cocoon. It is humanoid in shape, still moving. If the heroes free it (not before they kill or drive away the spiders), they meet a ... zombie!
The poor zombie wandered the dungeon alone, and tried to kill a big living creature (= a spider). The spider used the usual treatment, even if this victim did not look tasty. The zombie can be easily killed as any other zombie. It got but several doses of spider-poison, so can be something worth if it is extracted. You can mention to a druid or ranger the fact the spider had no poison anymore.
As they travel they notice a horrible rotten smell. As they travel it gets stronger and stronger forcing them to cover their noses and mouth less they choke on the horrible smell. Stream full of dead fish. Spawning trout die in mass quantities after they spawn littering areas with dead fish dying and deteriorating in the sun.
As they travel they notice a horrible rotten smell. As they travel it gets stronger and stronger forcing them to cover their noses and mouth less they choke on the horrible smell.A small goblin tribe preparing a wedding feast. The wedding is between two tribes as a gesture for peace, if the PC's intefere, feirce fighting could break out.
As they travel they notice a horrible rotten smell. As they travel it gets stronger and stronger forcing them to cover their noses and mouth less they choke on the horrible smell. Rotting animal carcass that has been ripped apart and tracks all over, covered in maggots.
In nature, for instance, a rhino has flies and ticks etc, that live on the hide and live off the blood. Rhino will visit and lie in ponds where turtles will clean the underwater portion of the ticks and a species of bird will clean the the top of ticks and other parasites. What if where the characters camp there were a species of animals that lived off wounds of the creatures. PCs camp. Anybody with wounds on there body are soon covered with small rodent - insect - shadows - whatever. Would immediately see it as a threat I would imagine. But perhaps one of the wounded didn't wake up when it happened, and when they did finally wake they were completely healed. Perhaps somebody was warned of something attacking them but they were able to notice that the wound was actually getting smaller instead of larger. Or maybe they successfully beat the creatures off them and don't notice an improvement, marking this place never to rest at ever again....later learn that villagers send their wounded there but they keep it a guarded secret because they don't want all the attention or traffic and what comes with such a special gift. Could turn into something more too if characters decide to start blabbing about it.
A revolt or attack happens against a strong city/kingdom. All the losers of the battle that can be captured are brutally crucified along the roads that enter the kingdom to show their strength and as a demonstration of what happens to their enemies. ... a long road, decorated with hundreds of dying crucified soldiers... You see them bleeding, you hear them screaming and whispering for help. Do you really want to enter this reportedly peaceful kingdom?
Herbalist in the group mistakes one plant for another and mistakenly poisons the group. Not to death, but pretty darn ill with recurring symptoms until the cause and cure are realized. (Local people may be able to help rather easily. "You ate Dragon's Rot you fool, looks and smells just like mint except it has these small thistles on the root. Only grow in the Hornwood Forest, that must be where ya got them. Eat this and you will feel better in 4 hours."
PCs camp for the night in a dry pine forest. Fire skill of the person that made it is usually pretty good, but during the first watch the unexpected happens: a spark lights the surrounding woods and a brush fire quickly starts. Be quick or it could turn into a disaster that could affect the entire region.
Real World: some Indians in the Amazon treat their eyes with a traditional potion applied with palm leaves. Brutally painful, the drug alters vision, giving the jungle's dense green walls greater texture and dimension. You could adapt this to desert or swamps, or other hard to navigate regions.