A great (if super touristy) way to enjoy the scenic Rhine valley, the KD cruises give you both…read moreshort-trip, and all-day excursions, as well as one-way or round-trip options. They start up north in Köln and end in Mainz, with stops at nearly every lovely little Rhein town along the way. You can buy your ticket at the booth by the gangway where the boat docks, and the price varies, depending on how far you're going and if you are making a return trip. I've been on this line a couple of times now, once in '96 and once this summer, and it's pretty much exactly the same.
On the boat, you have different seating and standing options. There is an indoor deck with dining tables and air conditioning. There is a main outdoor deck with patio chairs that people rearrange to their preference and a snack bar where you can purchase beer wine and soft drinks, as well as würstchen, chips, and a few other items (at a premium captive audience price, of course). There is an additional upper deck that is for standing only. The weather the day we went was gorgeous and we were going to be on a plane home the next day, so we opted to hang out on the top deck during our 4-hour trip from Boppard to Bingen. I imagine the indoor deck is popular on rainy or cold days.
A pre-recorded explanation in multiple languages (German, English, and I think Spanish -- possibly another) comes over the loudspeakers as they pass different landmarks and points of interest. They even play Die Lorelei (famous German folk song) as you sail past the Lorelei. It isn't particularly clear and easy to hear when you're outside, but you can at least hear the names of the points of interest, so you can look them up later if you so wish.
If you want to meet fellow Americans and their families while you're on your trip, this is a place to do it. It's also a great place to people watch and guess what the relationship is within certain groups traveling together on board. You will most assuredly be taking photos for other people as well. Overall, it's worth the time and money to travel the Rhein this way, and I'd definitely recommend it to first-time visitors to Rheinland.