Boat tours are held along the river between the towns of Krems and Melk. On the tour, which lasts around 2 hours, you can sit outdoors on the boat and watch comfortably around. Complete your tour with views of the castle, vineyard and garden. I was staying in Vienna for work while I did this tour. It was nice because it was July, and it was pretty hot. Guidance is also being made on the boat. Even in German, information about the name and history of the castle you were seeing on the shore at the time is given.
It takes an hour's train ride to get here from Vienna. You can start the tour from Krems or Melk and finish at the other. You can reach both towns by train from Vienna. Train times and ticket prices can be viewed at http://www.oebb.at. If you live in Austria or need to be there for a long time for work or if you want to spend a holiday there, it's a trip I can recommend. Not only are there convenient routes for boat rides, but also for hiking or cycling in the surrounding area.
Plenty of travel days
Bay