Scientific American features an interesting article on the Large Hadron Collider, a particle accelerator being built 100 meters underground near Geneva, Switzerland.
When complete, the particle accelerator will enable physicists to study sub-atomic particles, explore new forms of matter, and test theories about our universe and the fundamental physical laws of nature. You can learn more about the United States' involvement in this international project at this beautiful website.
How does a particle accelerator work? From the LHC website: "Inside the accelerator, two beams of particles travel at close to the speed of light with very high energies before colliding with one another. The beams travel in opposite directions in separate beam pipes – two tubes kept at ultrahigh vacuum. They are guided around the accelerator ring by a strong magnetic field, achieved using superconducting electromagnets. These are built from coils of special electric cable that operates in a superconducting state, efficiently conducting electricity without resistance or loss of energy. This requires chilling the magnets to about ‑271°C – a temperature colder than outer space! For this reason, much of the accelerator is connected to a distribution system of liquid helium, which cools the magnets, as well as to other supply services."
Closer to home, Fermi National Laboratories operates a particle accelerator in Batavia, IL. The Fermilabs website has information on tours and outreach events.