The 2 km diameter tunnel of the main accelerator at the Fermi National Accelerator Laboratory (Fermilab) in Illinois is buried underground, but is marked by a service road on the surface. The Tevatron, as it is known, is designed to acceler- ate protons up to 1000 GeV (1 TeV). In 1985, it was modified to operate as a collider, with protons circling in one direction, antiprotons in the other direction. The main laboratory buildings are to the left of the ring, dominated by the high-rise administration building. The land within the ring has been restored to natural prairie by volunteers. Chicago lies in the distance at top.