Wikipedia’s Book Tower entry says that:
The Book Tower is an Italian Renaissance styled tower in Detroit, Michigan. Construction began in 1916 as an addition to the original Book Building and finished a decade later. Designed in the Academic Classicism style, it is 475 feet (145 m) and 38 stories tall (not including two basement levels), with two mechanical floors at the top encasing the green copper roof, a roofing style shared by the nearby Westin Book-Cadillac Hotel. Retail and gallery floors used to reside on the first and second floors, with businesses previously occupying the rest. Sadly, as of 2009, the building is unoccupied.
Named after the famous Book Brothers of Detroit, it was briefly the tallest building in the city until the completion of the Penobscot Building in 1928. A taller Book Tower of 81 stories was to be built at the opposite end of the Book Building, but the Great Depression cancelled those plans.
The Book Building and Book Tower are now completely vacant. You can get a map to the Book Tower from Wikimapia. Emporis has more about the Book Tower and also more of the buildings designed by architect Louis Kamper. If you’re wondering about the Penobscot Building, Michigan in Pictures has that covered.