The 15 toughest stretches of holes in golf\nThe Wells Fargo Championship returns to Quail Hollow this week, a course that boasts the notorious "Green Mile." While the course's famed three holes can be a trial, it begs the question: Where does it fit among the toughest stretches in golf?\nNamed for Jack Nicklaus, who redesigned the course, PGA National's 15th, 16th and 17th holes are more than a marketing ploy: At the 2015 Honda Classic, there were 145 birdies at the Bear Trap against 299 bogeys or worse.\nCoined by Herbert Warren Wind, Augusta's 11th, 12th and 13th constitute the most famous three-hole stretch in golf. While the 11th (the hardest hole during the 2015 Masters at 4.326 strokes) and 12th (3.125 strokes) live up to their tenacious reputation, the 13th has ranked as the easiest hole the past two years. Of course, the accuracy and distance required by Azalea's tee ball perennially makes the drive one of the most important -- and for viewers, exciting -- shots during tournament.\nThe par-3, island-green 17th is one of the most famous holes in the world. But it's merely a part of TPC Sawgrass' closing puzzle; the 18th hole is actually tougher, boasting a +.397 scoring average during the 2015 Players, the highest number on the course. The par-5 16th was once a true risk-reward endeavor, although advances in club technology has rendered the 16th defenseless (it conceded 17 eagles last season).\nLike my man Indiana Jones, I battle ophidiophobia, so let's get through this quick. Copperhead's final three holes -- two 440-plus-yard par 4s, with a 215-yard par 3 sandwiched in between -- is not necessarily a stretch to conquer; rather, a player just wants to get through unscathed. The 16th is the most grueling, coming in at 475 yards with water running up the right side. Not that Jordan Spieth had any trouble: During a playoff at last year's Valspar Championship, Spieth made 4 at Nos. 18 and 16 before converting a birdie at the 17th to win.\nHow about this for a finish: A 508-yard par 4 whose green is guarded by a lake on the left and bunker on the right; a 220-yard par 3 with a peninsula green and sand in the front; a 493-yard, uphill par 4 with a creek running up the left and bunkers scattered throughout. The numbers back the description up, as the 16th, 17th and 18th ranked second, third and first in scoring difficulty at the Wells Fargo Championship in 2015.\nHow brutal is the three-hole stretch on Colonial's front nine? So graphic that we can't even show you a picture...At last year's Colonial Invitational, Nos. 3, 4 and 5 holes ranked second, fourth and first in difficulty. The Horrible Horseshoe is highlighted by the fifth, a 480-yard, dogleg par 4 hugged by a creek and tree line. Dan Jenkins included the fifth hole for his book The Best 18 Golf Holes in America.\nBethpage has the infamous first-tee warning sign, the picturesque par-5 fourth hole, and the 15th ranks as one of the hardest holes in U.S. Open history. Yet, the start of Bethpage Black's back nine -- a trio of par 4s with a cumulative distance of more than 1,400 yards -- ranks as the course's toughest stretch. At the 2002 U.S. Open, the field was +1.397 over par on holes 10-12.\nIn Jean van de Velde's defense -- that's something you've never heard -- it wasn't like the Frenchman collapsed on an innocuous hole. In 2007, the last time the claret jug was contested at Carnoustie, the 18th ranked as the second-hardest hole in golf for the entire season, as players averaged a 4.611 score on the 487-yard, burn-and-bunker infused finisher. The 16th (a 250-yard par 3 with four bunkers and undulated green) and the 17th (creek-crossed 460-yard par 4) are no cake walks, either.\nMost know Oakmont for its church pew bunkers, or No. 1's reputation as the hardest opening hole in the game. Yet, it's a four-hole stretch from the seventh to 10th where Oakmont's competitors get run through the wringer. At the 2007 U.S. Open, the average -- repeat, AVERAGE -- player went this gauntlet in two over par.\nTheoretically, we could just nominate the entire course. When it last hosted the Open in 2013, seven of the toughest 20 holes in golf that season came from Muirfield, with 10 ranking in the top 50. The Nos. 14-16 stretch is particularly sadistic: Length, unforgiving fairways and diabolical greens translated to a +1.116 over-par scoring bump at the 2013 tournament, making eventual champion Phil Mickelson's performance here (birdie-par-par) all the more impressive.\nThe last three winners of the Memorial Tournament own a collective 40-under score, leading one to believe Muirfield Village can't be that tough. The course's last three holes speak otherwise: A 200-yard par 3 over water; a suffocatingly tight 478-yard par 4; and a dogleg, uphill, every-obstacle-you-can-imagine 484-yard finisher are the type of closing stretch that keeps players up at night. All three ranked in the top-five hardest holes at the Memorial last year.\nCan a third of Shinnecock be classified as a stretch? We'd vouch for yes, especially given its diverse nature from the rest of the course. The 2004 U.S. Open field's average score was four over par for the competition. The route from the sixth tee to the 11th green left players 2.1 strokes over, highlighted by Shinnecock's four toughest holes (Nos. 6, 7, 10 and 11) in this span.\nThree of AAC's hardest four holes come in this route. Two par 3s more than 200 yards, with the par-4 16th coming in at 440 and the 18th at 490, will do that to a golfer. The par-3 15th was especially challenging for the 2001 PGA Championship field at +.342 strokes, which is what made David Toms' ace so noteworthy when he won the Wanamaker Trophy in 2001.\nThese holes are nicknamed the "Cliffs of Doom." Enough said.\nWhistling Straits' merits as a punishing track took a hit following Jason Day's record-breaking conquest of the Wisconsin links. However, not every hole was for the taking. The 17th and 18th added +.724 strokes to a player's scorecard last August. Apropos, then that the holes' names are "Pinched Nerve" and "Dyeabolical."