Every now and again we encounter a retrofuturistic urban planning proposal that is equal parts whimsical and hilarious, such as the proposed million-person city spanning from New York to San Francisco. Here's something that eclipses that design in terms of comic impracticality. Behold Oscar Newman's 1969 plan to hollow out an entire, nuclear-resistant city under Manhattan. How on Earth would all of this space be made? Why, by burying nuclear weapons deep underground and detonating them, of course.