Nienburg is a small Weser town between Hannover and Bremen, old enough to have a proper centre and modest enough not to overplay it. The streets around the market square hold half-timbered houses, brick facades, St Martin's church, and the kind of quiet northern German order that makes a slow walk pleasant rather than dramatic.
Its most distinctive identity is asparagus. Nienburger Spargel is the local pride, and the Lower Saxony Asparagus Museum treats the subject with cheerful seriousness. The wider Nienburg Museum is based in the Fresenhof, a handsome old Burgmannshof that gives the town's history more depth than the shopfronts first suggest.
Nienburg is not a major German stop, but it clears the spare-day test if you are already in Lower Saxony or cycling the Weser. Spend the morning in the old town, visit the museums, then follow the river path along the Weserwall before dinner somewhere serving asparagus in season.