Henry Lim struck out to design and build what could arguably deemed the pinnacle of Lego structure—a working Harpsichord. With the exception of its wire strings, the Harpsi is built entirely out of Lego. The 100,000 piece instrument would likely have one of the largest manuals of tiny, annoyingly difficult-to-understand isometric diagrams to date, but the project page does a rather good job of explaining the process he undertook to build such a thing. It also features an MP3 of the harpsichord in action.
Project Page [HenryLim via MAKEblog]
