Free admission. Summer hours open everyday at 10am. Winter hours Monday - Saturday 10am to 5pm. The Thunder Bay National Marine Sanctuary preserves a national treasure, nearly 200 historic shipwrecks in and around the bay. Lake Huron's cold, fresh water preserves many of these shipwrecks intact and in water depths ranging from a few inches to 200 feet, making the sanctuary a popular destination for divers, snorkelers and kayakers. You can explore the history and archaeology of these wrecks at the Great Lakes Maritime Heritage Center, the Sanctuary's 20,000 square foot, river-front headquarters. Exhibits on Great Lakes maritime history and shipwrecks include the new "Exploring the Shipwreck Century" exhibit, a 9,000 square ft. permanent exhibit featuring a life-sized recreation of a Great Lakes schooner and a shipwreck site. Visitors may also enjoy artifact displays, and interactive learning stations on technology and diving. The Center also features a sanctuary store, state of the art education spaces, high-definition theater, and archaeological conservation lab. Wreck locations are available on our web site. While visiting Alpena, you may want to explore the Thunder Bay Sanctuary Research Collection, one of the largest archival collections of Great Lakes maritime history, located at the Alpena County Library.