For the price of the Iraq War, we could've built a undersea subway beneath the Atlantic Ocean and the Mediterranean Sea from New York to Rome.
The 31.35 mile Channel Tunnel, built from Folkestone in England to Calais in France, cost 4.65 billion pounds in 1985 prices, or $18.8 billion in today's dollars. This comes to $600 million per mile. The distance from New York to Rome is 4280 miles. At the price of the Channel Tunnel, we could've built a railway underneath the Atlantic and the Mediterranean between these two cities for $2.57 trillion, which is less than Joseph Stiglitz and Linda Bilmes' estimate of $3 trillion for the total cost of the Iraq War.
Image from Kdoug at Daily Kos.