Skyrim is a game that feels suitably epic for most of the time, but if there's anything that can make it feel even more epic (as if that were possible) is this mod that turns all of the game's trees into giant redwoods.
Through the Bigger Trees mod by xweto, even the tallest Nord will feel dwarfed by these majestic giants, which replace the game's existing trees with big ones. You'll feel like you're walking around in Fangorn in Middle Earth.
Keep in mind that the mod compatible with the Skyrim flora overhaul and a few other add-ons which modify the trees and landscape in Skyrim, but you'll need the latest versions to get them to play nicely together.
Users have reported slowdowns with the mod, so you'll need to have a pretty beefy system to get it to run well.
That being said, if you can run it, and you enjoy the thought of walking through a Skyrim populated by giant forests, this mod's well worth picking up for the experience alone.
Grab it off the Skyrim Nexus here.