Our family will be traveling by car from Nuremberg to Vienna via Passau, planning to visit Mauthausen Memorial and Melk. Overnighting in Linz.

It sounds like there are extensive bike paths along the Danube and perhaps walking as well.
Can someone recommend a good walking loop perhaps from or near Melk that would be scenic and pleasant (travel day is either May 12 or 13). It wouldn't have to be a circular loop but if we can walk to a major landmark that might be a bonus.

Thanks for you help!

Walkers can use the bike paths also- these are paved , well marked and on both sides of the Danube.

perhaps 1 idea is to taake the pathway on the right side of the Sanube from Melk and go downstream -

nice views - you pass Schonbuhel Castle immediately on the rive r( probably not open but try anyway - further along is Aggstein Castle- this hogh above the river and a good hike up to it but worth it- then continus along the river to an area just across from Spitz.
There you find a ferry boat to take you across the Danube ( this with no motor only uses the danube current ) Spitz - a nice wine village - - bus or boat back to Melk

boats

www.ddsg-blue-danube.at

www.brandner.at

bus
www.vor.at

perhaps just a little longer than intended but worth it in my opinion.

also look to
www.wachau.at

www.donau.com