Jazzinstitut Darmstadt is one of those wonderfully specific Darmstadt stops: a serious public jazz archive tucked inside the Bessunger Kavaliershaus, a baroque hunting lodge from the early 18th century. Its collections of books, periodicals, recordings, photographs, and documentation make it a working research centre rather than a casual museum.
For most travellers this is a specialist detour, not a must-see. But if jazz matters to you, the institute is more interesting than its modest opening hours suggest, and its "Voices of Change" events occasionally turn the archive into a live cultural venue. Check ahead before going, because the public-facing hours are limited.