I had my first round interview through my university which was as simple as interviews go with some easy behavioral questions asked by a friendly interviewer. Nothing that i can think of that made my first round interview difficult. I got the second round interview in Richfield, MN which was a lot more difficult than the first. It was a set of 3 interviews with 2 interviewers each. They asked normal interview questions aswell as much more difficult ones. After all three interviews and presentations and tour i was on their beautiful campus for over 4 hours.