It's not the kind of engineering milestone that anyplace wants to have, but the Russian city of Yekaterinburg has learned to live with it—the world's tallest abandoned structure. As kuriositas.com explains, the 720-foot tower that dominates the landscape is actually a half-finished TV tower. Soviet engineers started working on it in 1981, but got only halfway up to the intended height when the USSR collapsed, along with work on the project.
Best part: The tower now has a slight lean because of engineering mistakes, though it's not in any danger of falling. The city has had to seal it shut because of the number of suicides and (not-always-successful) base jumpers it attracted. But things might change: Yekaterinburg is now soliciting ideas from developers around the world to turn their leaning, abandoned tower into something of actual use.