"On the morning of June 15th, Guy Burckhardt woke up screaming."
Tunnel Under the World by Frederik Pohl (13MB MP3)
Form the old time radio show X Minus One here's Frederik Pohl's classic sf story, "Tunnel Under the World," (Galaxy Science Fiction, January 1955.) This is one of the best stories from the Golden Age of Science Fiction, in addition to being one of the trippiest. It's like a prototype of the kind of mind-bending tales that would later be associated with PKD.