Rock Island Arsenal Museum

Floating in the Mississippi River, Rock Island once held a Civil War–era arsenal and POW camp. It's now the site of the impressive Rock Island Arsenal Museum (with old guns galore), as well as a Civil War cemetery, national cemetery and visitor center for barge viewing. Because the island is still an active army facility, it is only open to US residents with photo ID; you must first go through a security check at the Visitor Control Center to obtain a visitor pass.