I really enjoyed interviewing for the Explore Microsoft Internship! The process took about three months. First, I dropped off my resume at the Computer Science Career Fair at my university, and was contacted a few weeks later to do a quick phone interview. The phone interview was mostly behavioral and not too difficult. A few weeks after the phone interview, I was contacted to do an onsite interview at Microsoft in Redmond.
The trip to Washington took three days, and Microsoft paid for absolutely everything - my flight, my hotel, my taxi rides, a generous meal budget, and a tourism stipend. The first day was primarily travel, followed by an informal dinner on campus with other interview candidates. The second day I was scheduled to interview in the afternoon after lunch. I did three interviews in three hours. The first was technical (coding on the whiteboard), the second a mix of technical and behavioral, and the third behavioral. I heard from other candidates that the type interviews and questions asked varied a lot. On the third day, I had a little time to tour Seattle before I took a flight home.
A week after the interview, a recruiter called and offered me an internship. Their offer was quite generous, and I was happy to accept.