Probably the most fun you can get from an internship. The Yelp Internship Program (YIP) is awesome, and they really help you explore the city/surrounding areas by providing events and weekend ideas. Perks are pretty standard: snacks + drinks, foosball, pool, free in-house coffeeshop (especially the chai latte).
The work is very team-dependent. On Search, you work on pretty cool projects that cover a lot of different disciplines. Some of the other interns didn't like their projects too much, and a lot of people were placed on a different team than what the recruiter said. Mentors are hit-or-miss, but there's definitely a lot of opportunity to learn.