Absolutely amazing interview experience. Think of it as telling them stories about yourself.
The first night is a dinner where you meet most of the managers that are taking part in the interviewing process. Food is provided with an informative presentation about Progressive itself, and about how exciting the Cleveland area is.
The next morning you'll have breakfast, presentations by folks at Progressive, a meetup with some new hires, 2 interviews with a break in between, lunch, and also a quick tour. The questions are mostly behavioral, but you can of course make references to the technical work you have done in the past.
Also, they reimburse you for everything (trip related).