Frankfurt is Germany's "all business" destination. After WWII, most southern Deutschland cities savored and fortified their existing infrastructure--buildings, etc. Frankfurt decided to start anew. So, although a church and building here and there may still stand and serve as a reminder to times past, most Frankfurt architecture and infrastructure is modern and unique.
As a commercial hub, Frankfurt bustles during the work-week, but the city center becomes sparsely populated on weekends. Most downtown stores even close on Sundays. Leisure tourists are a much more common sight across Germany in cities like Munich, Cologne, and Berlin.
Still, if business brings you to Frankfurt, we've got your healthy lifestyle options covered.