Dayton Street Historic District is Cincinnati's old millionaire's row, lined with 19th-century houses that show how wealthy the city became before the Civil War. It is quieter than Over-the-Rhine and less famous than grand residential streets in Chicago or New York, but the intact run of mansions gives a clear sense of Cincinnati's boom years.
Come during daylight and treat it as an architecture walk rather than a single stop. It works well with nearby West End and Over-the-Rhine sights.