The Frigid Outskirts in the most recent Dark Souls 2 DLC, Crown of the Ivory King, was incredibly challenging. It's hard to capture the essence of it without playing it, but it's truly fucked. You walk through a frozen wasteland in the middle of a snow storm. When the storm is raging, you can see nothing but white, it's even hard to tell where the ground is and whether you're changing elevation. Every few minutes the storm will briefly subside, allowing you to see how off track you've gotten, and for you to see the meager and pathetic landmarks scattered around the massive, indistinguishable map. Apart from white snow the only landmarks are a few broken down buildings, each a good mile apart.
Navigating a huge area under conditions such as these would be a challenge in itself but of course there are enemies. Nearly without warning large black horse creatures will come galloping out of the snow with their horns lowered in a charge. I say nearly without warning because the only warning you do get is the faint sound of hooves about one second before their horns make contact with your body. They also fly. And shoot lightening. Often, they will attack in packs as well. The damnedest thing is that even when the storm subsides and you're granted a brief look at the environment you're traversing, there will be no horses in sight. It's almost as if they materialize out of the storm itself.
The map is so big that even without the storm and without enemies it would take almost ten minutes just to run across the entire map. The storm and enemies easily triple that time. It's not uncommon to defeat one of the infuriating horse creatures, and then find that you've completely lost your bearings and haven't a clue which way you've come from and which way you've gone. You then have the option of waiting out the storm safely, wasting valuable time (horses seem to appear without warning randomly, even while you stand still) or to proceed in the direction that feels right in the hopes that when the storm clears again you'll be closer and not farther from your destination. Unfortunately, it's not uncommon to spend 2 minutes walking in a totally wrong direction, fighting horses along the way and consuming your valuable and limited healing supplies.
To top it all off at the end of this unforgiving area is an incredibly hard boss: two huge fucking cats that will relentlessly leap and swipe at you. If you kill one of them, the second enrages and begins regenerating and gets a hefty increase in damage. Until you master the Frigid Outskirts, you'll count yourself lucky to arrive at the boss with no healing items and your two companions dead. Because to make it to the boss at all is a feat at that point.
This was all especially hard for me because I was on NG+++ when the DLC hit. It took me a good two hours or so just to learn the ins and outs of the map, and how to kill the horse enemies without getting murdered. After practice I was able to quickly and safely make it to the boss. I had a lot of trouble with the boss though. All the players I would summon to help me would get one shot by the bosses, leaving me to try and fight two huge cats on my own. I ended up beating the bosses with the NPC summons, after another two hours of attempts. It was damn satisfying though.