From Merion to Oakmont to Torrey Pines to Pebble Beach, these 18 holes provide the toughest test for U.S. Open golfers

Every year, the U.S. Open provides the most challenging conditions on the hardest golf courses in the nation. But which 18 holes rank as the toughest of the tough? With the help of Tom Watson, Rees Jones and a couple of golf historians -- and armed with USGA stats -- I compiled the Agonizing 18. My story for ESPN.com's golf section in advance of this year's Open. http://www.espn.com/golf/story/_/id/19553043/imagining-course-18-most-merciless-holes-us-open-history