There are some architectural interests in studying in St.Louis.

• The Mississippi mound-builders from the prehistoric times, built mounds.
• The city's massive population explosion in the 19th century led to hard learned lessons in urban planning and infrastructure.
• The Wainwright building, considered by many architectural historians to be the first "skyscraper" was built here and still stands today.
• The Worlds Fair in 1904 kicked off the City Beautiful movement, which set a neoclassical standard for civic and public buildings that deeply impacted the architectural styles of the US. 
• Pruitt-Igoe, the public housing project infamous to architects and planners, was unveiled and given many architectural awards as a Modern architecture solution to the urban poor. It was demolished 20 years later as a failure after crime, extreme poverty, abuse, and neglect spiraled.
• The iconic arch, built by architect Ereo Saarinan, is located here, and is pretty cool looking. One of the senior partners of my architecture firm told me that when he was a student in St.Louis, one of his friends' aligators died, they put it in small coffin and buried it under the planned apex of the then in-construction arch with a small funeral. Alcohol may have been a factor.
• The city straddles the border of its own state, which is very odd to me, having lived in a state where the distance one has to drive to reach the state border would cross several eastern seaboard states.
• Not so architectural, but certainly work-generating: apparently St.Louis is the largest city to be repeatedly struck by lethal tornadoes.
• If one measures a city's vitality by its population increase and decreases, St.Louis shone most brightly in the early 1900s. Following the slow decline of industry and the rust belt, the population of St.Louis fell by half between 1950 and 2000. This alone creates what I consider very interesting conditions. What happens to a city when half the people just leave? However, it is also representative the more recent phenomenon of inner city gentrification. Educated, wealthier, mostly young, moving out of the 'burbs to the inner city. This has the overall effect of making the suburbs poorer, with higher percentages of minority groups as well.