One of the wonders of the Morris Arboretum (at the U. of Penn. in Philly) is their newly created "Summer Palace" sculpture by North Carolina artist Patrick Dougherty. Made entirely of natural materials locally acquired and no nails or hardware of any kind, this three-story Russian-themed structure was built with the help of 75 volunteers over the course of 19 days this spring, is and expected to last two years.
Aside from its obvious aesthetic appeal, I love that the design came to Dougherty spontaneously as it evolved, and that all those volunteers had the fun of being part of its creation. The whole process is chronicled on a blog, Patrick Dougherty at the Morris Arboretum.
The Morris has quite a collection of more permanent scultpure, as you see on this page. While the choice of sculpture pieces for gardens is often controversial, I'm always happy to see the effort being made because once in a while the results are as spectacular as this.