Here's my favorite: The Lady Landfill. From the surface, all you'll see are these tiny islands.
But when you dive beneath the surface, you'll find this:
The Lady Landfill was designed by three Serbian architects, Milorad Vidojevic, Jelena Pucarevic and Milica Pihler for the eVolo 2011 Skyscraper Competition. The giant skyscraper would collect and recycle the waste of the Great Pacific Garbage Patch into an energy source.