Looking for an unusual way to spend your Saturday? Why not check out Yerkes Observatory, 373 W. Geneva St., in Williams Bay, near Lake Geneva?

Situated 190 feet above Geneva Lake, the observatory is a fascinating place in an architecturally interesting building and offers great views of the surrounding area.

A research branch of the University of Chicago's Department of Astronomy and Astrophysics, the historic building, located on a 77-acre park, serves as lab space and offers telescopes for research and teaching.

In addition, a large part of the University's astronomy library is housed there. Considerable research is conducted at Yerkes, as are many public outreach programs. For full details on these, visit the Yerkes Web site.

Yerkes Observatory was the pet project of Charles Tyson Yerkes, a Chicago transportation bigwig. Yerkes financed a plan developed by George Ellery Hale. The centerpiece of the building was, as it still is, the 40-inch refractor telescope, which is now, as it was then, the world's largest. Hale was the founder of the American Astronomical Society and co-founder of the Astrophysical Journal, headquartered at Yerkes until 1965.

When visiting the building, be sure to walk the lovely park-like grounds and bring binoculars to get an up-close look at the decoration on the building's exterior. Designed by Henry Ives Cobb, the building is a product of his love for classical mythology. His terra cotta ornaments include signs of the Zodiac, phases of the moon, unusual animals both real and imagined.

Inside, in addition to tours (see below), the observatory has a gift shop and wall displays explaining -- in words and pictures -- Yerkes history, comets, galaxies, nebulae and the death of stars.

In the southeast transept, on the main floor, is the Quester Museum, which celebrates Yerkes astronomers who have profoundly impacted the scientific world and the local community over the past 100 years. It pays special attention to the links created and maintained by Yerkes and the Williams Bay community over the years. The Quester is the fruit of the work of area volunteers interested in local history.

Tours of the observatory take place every Saturday morning at 10 a.m., 11 a.m. and noon. There is no admission fee, but a $5 donation is suggested. Tour guides offer information on the history of the observatory, astronomical research and space.

Visitors will get a glimpse into the 90-foot dome, one of the world's largest of its kind, where the 40-inch refractor telescope is housed. Tours are intended for families and small groups and reservations are not accepted.

For groups of 15 or more, special programs are available, including viewing through the telescope, mini-classes, slide shows and talks. The charge for special programs is $100 per hour, per group. You must contact tour coordinator Richard Dreiser (262-245-5555) to make advance arrangements.

Yerkes has added weekday tours, too, though those are not free. The 30-minute tours are available weekdays (except Wednesdays) between 9:30 and 11 a.m. and 1:30 and 4:30 p.m. Advance reservations (contact Richard Dreiser) for these tours are recommended and they cost $25.

To get there, take I-43 to the Highway 67 Elkhorn/Williams Bay exit. Turn south onto 67 and drive about six miles to the intersection of Highway 50. Cross the highway and continue downhill almost exactly one mile. Turn right, and go uphill, curving to your left on Highway 67/Geneva Street, almost exactly a mile up to the unlit brown sign with white lettering that says Yerkes Observatory.