Be it a futuristic design, a pre-production model, or a technological showcase, the concept car is now a major part of the automotive world. Tens of concept vehicles are being released every year and many of them are downright spectacular. But the concept cars we see are just a fraction of the concept vehicles that are being designed or built behind closed doors. If you need proof, Porsche just published “Porsche Unseen,” a book that showcases design studies from 2005 to 2019. Three of them have been released online as well, and they’re as spectacular as they get.