Styrian Armory was the reason I went for Graz. Four floors full of weapons and armour. It is a must place for anyone who likes armour and 30 year war's armored cuiraissiers. Even the racks are from 1600.
You were not allowed to take photos, but here are few samples from the books I bought. If you go there, take the guided tour. I first 45 minutes wandered on my own and then took part in the one hour tour. That was a perfect way exploring the site.