Kolle 37 is not your usual kind of kids' recreation space. This 4,000-square-meter, anarchic adventure playground in the heart of Berlin's central Prenzlauer Berg neighborhood is like the love child of a Wes Anderson set designer and a steampunk doorman at the city's infamous Berghain nightclub. Also known as the Adventurous Construction Playground Kolle 37, this unconventional educational space allows children to build " or, indeed, destroy " structures as they see fit. (Parents can enter only one day a week, on Saturdays.) Kolle 37, which started in 1990, is open to children between the ages of six and 16, and offers a rare space for unaccompanied play and so-called "free-range parenting" " moms and dads are asked to give a cell phone number and leave the site promptly. The playground, which receives funding from Berlin government authorities, also offers practical courses such as pottery, blacksmithery, archery and handicrafts, and has a space for music practice. Weekly meetings are held among the kids to discuss rules and problems, with a system of cards used for behavioral issues. Yellows serve as warnings and reds mean a child must leave for the day, for example if they hurt someone or stole something. "They run everything," says [social workert Marcus] Schmidt. "If the government or officials visit, the kids give the tour. There's an equal relationship between children and adults here. This is a really, really special place."