Here is why Phil Mickelson calls this year's US Open course 'the hardest course we've ever played'

The U.S. Open kicks off this week and while this event is always the toughest of the majors, this year's has the added difficulty of being played at the notorious Oakmont Country Club.

In 2007, the last time the U.S. Open was held at Oakmont, only two golfers finished under par, with Nick Dougherty winning at 2-under. While going low is rare at the U.S. Open in general, to hear the players describe the course now, it sounds like this year's winner could finish over par.

Rory McIlroy recently called Oakmont "unbelievably hard." 

Phil Mickelson recently played some practice rounds and add that he thinks Oakmont "is the hardest golf course we've ever played."

There are a number of factors that make Oakmont so difficult. Below we take a look at the most menacing aspects of the course.