NUSearch, Northwestern University Library's search tool, can be used to find books and other library resources. To search for books, it is best to click on the "Books, Images, & More" tab; otherwise, you are likely to be overwhelmed with articles.
World's Columbian Exposition
"World's Columbian Exposition" AND architecture
poetry AND "classical influences"
"Hull House" AND theat*
"Chicago Board of Trade" AND building
Architecture AND classical influences
The advance search may be useful in certain instances: for example, you may want to limit your search to subject headings or other field. For example, searching "Chicago" in the subject field, and "architecture" anywhere, produces a much tighter search than simply entering <Chicago AND Architecture>.
It's also possible to click on "browse search" and browse titles, authors, or subject heading strings.
I'm regularly available in the Philosophy Department's Brentano Library (Kresge 3520) from 12:00 - 1:00 on Mondays, and in the Classics Seminar Room (Kresge 4364) from 4:00 to 5:00 on Tuesdays. I'm also always happy to meet in my office in the library by appointment: just click on the link above.