Route Wien -> Tulln an der Donau -> Wien  

I recommend to start on the Donauinsel right away - going through the city is boring and slow.

Donauinsel is an inline paradise - "Smooth like a baby's butt".

Greifenstein <-> Tulln section is on a rather harsh surface in both directions. It is almost perfectly even, but it's not tarmac, more like small stones rolled in concrete. Disturbing, slow, but rideable.

From the Donauinsel on, all on dedicated cycleways without cars, except for some road sections around Klosterneuburg.

The whole out-of-vienna path is part of Donauradweg so it is easy to navigate.

Took me around 6 hours in a cold and foggy November weather.