Has anyone taken this train before? I'm trying to figure out if I need to make reservations before I get there and if I should buy space in a couchette. Thanks.

I did it on the day of departure. I had no problem. This was in late June. The trip was about 10 hours. It was abit bumpy compared to the Paris-Madrid night train. I don't know why I bothered with a couchette because I would usually met other backpackers and we would paly cards until the wee...hours of the morning in the dining car. Enjoy your trip. The cost was about 55$ American dollars.