Army of the Damned is a 5e adventure that starts at level 1 and ends at level 5. It is set in Magic: the Gathering's world of Innistrad.
What is Innistrad? It's a setting steeped in gothic horror themes and makes liberal use of horror tropes. Werewolves hunt within the forests, vengeful spirits haunt the places of their grisly deaths, hedonistic vampires feast on humans at their leisure, and Frankenstein-like mad scientists create abominations stitched together from corpses. All these classic horror stories are merged together to create a unified campaign setting that is much more than the sum of its parts, an amazing and compelling backdrop for epic storytelling. I hear it shares many similarities to the D&D setting Ravenloft.
And here's the adventure:
Player's Guide to Innistrad: Human Variants (created by /u/Nihilates)
Map of Stensia (created by /u/Nihilates)
Map of Shadowgrange (created by /u/Nihilates)
Map of Mauer Estate (created by /u/Nihilates)
Geralf's Encoded Letter 3 versions: encoded, encoded worksheet (easier to read and work on), and decoded (created by /u/RanAngel)
Sir Delandel, the Undead Paladin (optional NPC to continue the adventure)