There are skyscrapers, and then there are skypenetrators. The X-Seed 4000 is one of the latter.
Conceived in the mid-1990s for a site in downtown Tokyo, the 'Seed is an eyeball-sucking ogre of a building (or "hyperbuilding," as these freakishly tall structures are sometimes called). At 800 stories tall, you could practically read a book cover to cover on the elevator ride to the X-Seed's penthouse. The company that planned to build it, Taisei Construction Corporation, never got around to erecting it; however, maybe they didn't want to. An Architectural Record investigation into the current state of the X-Seed quoted one building expert as saying, “It was never meant to be built. The purpose of the plan was to earn some recognition for the firm, and it worked.”