The Wasp's Nest
The thick heat of the afternoon drips sweatily through the rhodedendron branches and you are soothed by the monotone buzz of a million insects. When you finally emerge from the tangle of bushes, damp and scratched, you find yourselves in a curious grotto of rocks and decide to stop and rest. Sitting in the shade of a sizeable rock, it is several minutes before you realise that the monotone buzz has distinctly changed its nature. It's getting louder. A shadow passes over the sun. A flickery shadow, as if of beating wings. Into your mind leap unbidden images of furry, scaly, many-eyed, segmented creatures. Perhaps you should take cover.
There are many possible hiding places in this grotto. In a crevice, in amongst the rhodedendrons, in a hollow fallen tree trunk. Wherever the PCs decide to hide is where the giant wasp goes next (to its nest or to the flowers it loves to feed upon). Particularly unfortunate would be the encreviced PC who crawls further and further back, only to put his hand into a wriggling mass of giant wasp larvae.
By the looks of previous posts people seem to like bears in forests. Are they innocent, friendly bears? Or angry grizzlies? (Or lycanthropes, as Agar suggests)
You enter the clearing to find a huge and terrifying bear looming angrily over you. You instinctively draw your sword, trying to remember if you're supposed to act dead or act threatening. After a few breathless seconds of agitation, you realise that the bear is dead. It facial expression is not one of anger, rather one of contorted agony. It has been preserved and nailed to a tree.