The Adventures of Buckaroo Banzai Across the 8th Dimension (Movie)

Buckaroo Banzai and his mentor Dr. Hikita perfect the "oscillation overthruster", a device that allows one to pass through solid matter. Banzai tests it by driving his Jet Car through a mountain. While passing through it, Banzai finds himself in another dimension, and on returning to his normal dimension, he discovers an alien organism has attached itself to his car.