If you travel into the far Southwest of Skyrim, you'll find that the 'corner' of the region is filled with a huge mountain, on whose slopes are a staggering large number of dungeons, from mines to caves to ruins and even some outdoor instances. One of the most impressive of these is Lost Valley Redoubt, a massive outdoor 'dungeon' occupied by the Forsaken and a few Hagravens.
The primary way into the Lost Valley Redoubt is found off a small branch of river, where a waterfall comes down to make a pool. Near the pool are a pair of Nirnroot, close to where the dirt path fords the water, and a couple of mineral veins- iron ore further downstream and silver ore near where the waterfall ends. Gather these resources and some juniper berries from the nearby trees and then make a decision-
Are you a bad enough dude/dudette to take on multiple hagravens?
If you're less than level 30 and you neither operate as a sniper nor have a huge facility with magic, the answer is pretty much just 'no'. In this case, you can fight your way through the Forsworn with not much trouble, but you won't be able to finish up all the activities you can do here. Even with sniping skill, a good bow, and/or a really ridiculous amount of skill with magical wards, you can find yourself overwhelmed by the last few foes here, so be really prepared- and bring enough health potions to drown a mammmoth.
If you think you're prepared enough, save your game and move in.
Across the river, you'll climb some alternating steps and slopes until you see a cage hanging overhead. The man inside is unfortunately dead (despite often having been locked in a cage with a lockpick in his pocket) so take any stuff he has that you want from below. Moving around the outcrop that the tree he hangs from lives on, you will find yourself entering a ruins area. Be cautious here- a Forsaken Forager waits ahead on the path, though he's often distracted by using his grindstone, despite the second dead nord lying on the table next to him whose head and arm are flopped on the sharpening tool. Ambushing this Forsaken is your best bet here, and a very sure-fire way to stay safe, if you have a bow.
Be careful, though- as tempting as it is to close in, the right-hand half of the archway is underlaid with a tripwire, which will trigger a rockfall trap. Not only will this deal a staggering lot of damage to you, it will alert the forager at his grindstone and at least one other Forsaken who waits overhead with a bow. Just to make things worse, the overhead Forsaken have access to a lever that triggers another rockfall trap in a similar location a few meters further on, so if you're not cautious or sneaky you can wind up buried in a second avalanche.