Due south of Dragonbridge, near the edge of The Reach and Hjaalmarch, there is a tributary to the main local river. As you travel along it, you will find a small camp- two tents, a crate, a cookfire, and a boat- that appears to have been abandoned. In addition to a dagger, a few alchemical supplies, and a bit of food, you will find an item here- a journal. According to what is written within, a pair of travelers were investigating a destroyed caravan.
The caravan, from what the journal says, was torn up in a way that isn't like wild animals to do. However, the people in the caravan were all torn apart for no evident reason, and there wasn't any noteworthy thievery of goods. Because of this, the two travelers have followed the trail of whoever or whatever did this to the cave uphill, which they left camp to investigate and never came back.
This pretty much leaves it up to you to do something about whatever's been mutilating caravans.
Head up the hill following the trail that leads from the camp- but do so carefully. A cave bear waits here, outside the Depths, mucking about in the river to kill the local slaughterfish. Ambush or sneak attack the bear to slay it, and then feel free to collect the scales of the dead slaughterfish and the eggs from their nests, as well as the mushrooms and lavender growing around the mouth of the cave before entering.
The first thing you'll see inside is a narrow cave whose floor is shallowly covered in water. Across the water from you is a small dry campsite with what at first seems to be a sleeping adventurer on his cot- but he is actually quite thoroughly dead. Make a quick diversion to the right to grab some mushrooms from the end of the cave and then check the adventurer. His horker loaf and cabbage soup both sit uneaten beside his bedroll, and the chest that sits next to him is open- and empty.
Once you've checked the man for anything worth taking, advance along the cave through the water, taking time to grab the mushrooms that lurk here and there. Also pay heed to the ceiling- spiderwebs are all over the place in here, which is usually an indicator of frostvenom spiders in the area. This would also provide an explanation for the caravan assaulters dragging people off in addition to just killing them there- the spiders like to coccoon and save meals for later.
