There is a place in Berkeley which is amazing. It is called Adventure Playground. It is a "junk" playground which includes paint, paintbrushes, hammers, saws, workbenches and nails. Basically, kids can build things and have fun. The playground opened in 1979 and believe it or not (Because of legal liabilities of giving kiddos somewhat unrestricted access to tools and such), Adventure Playground is only one of four parks like it in the country:
Adventure Playground is an amazing place. It is a place that allows kids to dream and use their imagination. It is free and yes there are attendants there but for the most part kids are allowed to have fun and build.