At the turn of the 20th century, Downtown Brooklyn had a theater district to rival Manhattan’s. In the space of a few blocks near the Flatbush Avenue Extension, a collection of grand multi-use ballrooms and smaller vaudeville stages proliferated. Just a few decades later, most had fallen into disuse and disrepair, but in many cases, the buildings themselves survive. Here’s a look at a thriving entertainment district of days gone by — and the contemporary adaptive reuse projects reinvigorating its legacy.