If you like The Ruins by Scott Smith. . . then try...
Infernal by F. Paul Wilson
"The ninth entry in the Repairman Jack series. In this one, a shipwreck hunt gets very weird quickly."
Brimstone by Douglas Preston & Lincoln Child
"An FBI Agent investigates an art critic's murder, which points to the Devil as the culprit. Don't read this one at night without all the lights on."
Death of a Ghost by Charles Butler
"This sinister and chilling ghost story will appeal to adults as well. A creepy, supernatural thriller with a chilling twist."
World War Z by Max Brooks
"The book description says that this is based on extensive interviews with survivors and key players in the war. Since the author is the son of Mel Brooks, the reader never knows what to expect."
Ammie, Come Home by Barbara Michaels
"While not as overtly gruesome as the other entries on this list, this classic by Michaels, published first in 1979, is a satisfyingly scary ghost story."