http://www.nexusmods.com/skyrim/mods/74102/?
This mod adds a massive army of nocturnal zombies ghosts and skeletons that stalk the player if you forget to equip a torch while walking around at night at most places outside of cities. This makes exploring at night, frightening and dangerous. Most undead are numerous yet weak, the less numerous giant skeletons are very powerful, the ghosts immune to normal weapons. With optional harder nightmare mode. Be forewarned the giant skeletons on nightmare mode are extremely powerful, to the point even a very powerful player character is suggested to just run away from them, it's called nightmare mode for a reason.
Most undead are numerous yet weak, the less numerous giant skeletons are very powerful, the ghosts immune to normal weapons. The only places these undead won't follow you is into any town, city, store, temple, stewards dwelling, player house, orc stronghold, jail, inn, minor hold, major hold, castle, barrack, guild headquarters, city, barracks, military camp or military fort. Most of the undead are just regular mobs that stalk the player at night if you forget your torch and go too far from safer locations, though a few are colossal skeletons who are very very powerful, nightmare mode makes the colossal skeletons even more powerful doubling their massive health pool and giving them even higher damage. A Massive Burning Skeleton appears only on Fridays, that is a more powerful version of the Colossal Skeleton. Oh and if these undead for whatever reason somehow end up in sunlight, the damage from the sun will kill them.
Recommended mods to combine with this include Scary Ghosts which make all ghosts immune to normal weapons, darker nights, and anything that makes undead thingies look more scary... I also highly highly recommend NPCs protected redux so the undead things don't kill named NPCs. Their tendency to avoid cities helps, but they are numerous, and some of them quite powerful, so I highly suggest something like NPCs Protected Redux mod to be combined with this mod just in case. Yes this mod is at least partially inspired by the Hyrule field in Zelda with the skeletons that attack you at night time in Ocarina Of Time for instance, and and perhaps a few other games not to mention numerous movies and stories where scary things come out at night.
Night time in Skyrim never felt scary enough to me, torches never felt important enough, and I wanted Skyrim to feel a little bit more like a scarier survival game, hence I created this mod. It always did feel strange to me that the undead didn't seem to journey around at night.