The Prairie Avenue Historic District is a rich preserve of 19th Century residential architecture. All the bigwigs lived on the Avenue in its heyday, including the Pullmans, the Armours, the Fields and the Kimballs. And of course, the Clarkes and the Glessners, whose houses are the focus of these 1-hour walking tours. The Clarke House, built in 1836, is Chicago's oldest surviving building. It's really the only place in Chicago to see how an early Chicago family lived. The Glessner House, erected in 1887, is one of the most important residences in the world architecturally because it was designed by Henry Hobson Richardson (who also designed Trinity Church of Boston). The 1885, 27-room Glessner House epitomizes Richardson's revolutionary Richardson Romanesque style. Built for John J. Glessner, a director of International Harvester, this was one of Richardson's last designs and is considered one of his most mature. Glessner House is the culmination of his ideas of planning from the inside out. The L-shaped house and the attached coach house create a lovely courtyard. The tours are a wonderful way to learn about 19th Century Chicago. Both residences are museums--the Glessner House Museum nonprofit organization owns and operates the Glessner House (which received a $850,000 renovation in 1999) while the City of Chicago's Department of Cultural Affairs owns and operates the Clarke House.