Choose a specific place and a time in the past: the North Shore of Staten Island before the Verrazano-Narrows Bridge was built; the Back Bay area of Boston in the 1850s; Phoenix before air conditioning was invented; Seattle in the 1970s. Research this location, gathering as much information as you can about how it once was and how it has changed. Review public records, read newspaper articles, and peruse archival images. Local chamber of commerce sites and the Library of Congress's website are good places to start. Write a story set in the past in your chosen location, using the details you've uncovered to make it as authentic to that time as possible.