Canberra's National Arboretum is an ever-developing showcase of trees from around the world, with 94 forests of different species currently on site. It is early days for many of the plantings, but it's still worth visiting for the spectacular visitor center and the excellent views over the city. Regular guided tours are informative, and there is a brilliant adventure playground for kids.
The parking lot is paid. Admission to the park and guided tours are free.