Classic horror story
by H. P. Lovecraft
. It is written as a narrative
by a professor
who is trying desperately to dissuade
a forthcoming expedition
It makes very good reading, quite possibly Lovecraft's finest work, and an excellent resource for students of the Cthulhu Mythos, as one can find a good load of background information on many of the creatures therein.
It can also be found as an audio book, where the narrative has been converted to a radio interview instead. It's a bit shorter than the book, but still not bad.