Perhaps you've heard of Winter's Gem, and of the tragic fate of the Lady Karina. And perhaps not. It is, after all, a tale unspeakably old. Yet the Earth does not forget, and those of us who guard it do not wither...
Nine thousand years she has slumbered, while Winter diminished. So obsessed was He in her care, that He allowed Summer to run unchecked. His power dwindled, and Summer grew. There is a great unbalance in the world, young ones. One that I fear will break the back of the Earth itself, if not addressed. Winter must return. It is the Way.
A real-world location fit for filling out your adventure; where norse icelandic fishermen suffered unthinkable conditions throughout frigid winters to harvest the fruits of the ocean.
In the summer there is a small stone jail for those who are caught breaking the rules of the Sorcery Springs Geyser Basin, but in winter they are imprisoned within the warm waters themselves. No bolts or bars are needed, the cold takes the place of prison walls.
An insidious creature, most likely somehow "related" to trappers and lurkers, the Dead Leaves (for no other name exists as of yet for this foul thing), hibernates for three of the four year's seasons, deep underground. Its active time is Autumn, when trees shed their leaves, depositing colorful carpets across the ground. The terror then emerges and blends in with the surrounding leaves, perfectly camouflaged, waiting patiently for unsuspecting victims. In appearance it resembles nothing more than a ten foot square, six inch thick, layer of bright yellow, orange, and red leaves. The only hint that someone is walking on top of it, comes in the form of an unusual amplified sound of leaves crunching underfoot. Too late usually, the victims notice this additional "crunch". The Dead Leaves will then swirl and "rise" up to smother and suffocate the victim, like a colorful, malevolent, boa constrictor.
Fire, as can be imagined, is particularly effective against this creature, but one has to *know* it's there before putting it to the torch. And there's the rub. The creature is impossible to "identify" in a large patch of fallen leaves by eyesight alone.