tbabcock@timesrepublican.com TR File Photo Adventure Passes are once again available at the Marshalltown Public Library, allowing for free family visits to the Blank Park Zoo, Science Center of Iowa, Greater Des Moines Botanical Garden and the Waterloo Grout Museum. Known to be a place for checking out books, the Marshalltown Public Library is also offering free passes to the Blank Park Zoo and other Iowa attractions to check out. The Adventure Pass is one of the library’s best kept secrets, Youth Services Director Joa LaVille said. “It’s not meant to be a secret, but I would say it’s kind of a best kept secret,” LaVille said.