The jewel from a military perspective, apart from the defensive walls and towers, is the Reichstadtmuseum. This is cited in the old monastry buildings and has a good collection of arms and armour items, stretching from iron age to the Thirty Years War. I purchased a photography pass (only 3 euro) to allow me to take what I wanted, which I'd recommend if you ever visit. Some items were tricky to get due to the glass cabinets, but they do publish an arms catalogue.
These are the medieval highlights for me. I'll let the pictures speak for themselves, but there are some remarkably well preserved swords and daggers, in quantities that I'd not seen before outside of a state armoury collection.