The Misty Mountains. Sure, you might get waylaid by orcs, but otherwise pretty easy to cross. Just stock up on food before you leave the Shire. I feel we should change that. In the book, and movie for that matter, the Fellowship can barely cross the mountains, and it's not easy for the company in the Hobbit either.
My idea is, the frost effect from Forodowaith is added to the Mountains. And 'blizzards' are added. Just snow but faster and the frost effect is increased. If it's not a thing already because it caused problems or anything, the snow piling thing would be made use of; You know, that thing where you can stack the snow piles ontop of each other. These would also be like quagmires, but instead of suffocation would instead induce the frost effect (but faster). In addition, this wouldn't effect Elves. This idea would help improve the dangers of the Misty Mountains, especially if those Orcs you've been dreading suddenly appear.