Day trips from Vienna by train

I haven't done the bus, but I have biked it and then taken the boat from Krems back up to Melk. Both were worthwhile and done in one day, though I stayed in Melk. It still would have been possible to take the train from and to Vienna on the same day, it just makes a longer day. The bus is likely faster.

The daytrip to Melk is quite common and OBB has a special ticket package for it. You should search the forum for people who have done it.

I have done the package that Phred referred to. It includes train ticket to Melk, entrance to the Abbey, boat ticket for the Danube cruise to Krems, and train ticket from Krems back to Vienna. It was well worth it for me to have all the transportation taken care of before I started out. You have as much time as you need for the Abbey at Melk because the boat tickets are good for any of the boat times, just as the train tickets from Krems are good on any train going back to Vienna. I highly recommend doing the day trip this way unless you really want to bike or bus to Krems instead of the Danube cruise - some people prefer to do that. Also you can get off the boat at Durnstein if you want and then take a bus to Krems to catch the train - but for me that was just another time table (bus) to worry about, and the longer on the river the better for me.

Tigerfan, can you rent bikes in Melk and then return them in Krems?

Bike rental in the Wachau area:
https://www.nextbike.at/niederoesterreich/en/

Thank you for the bike rental link!

Yes, you can. We left our bikes locked up at the racks at the boat docks. I think we use Wachaubike.at and they delivered the bikes to our hotel. Our original instructions were to leave them at the train station, so I think you can do either.

But on another trip (I have done this twice) we used free bikes from our hotel and brought them back to Melk on the boat with us.