The Danube bike trail offers a wide variety of scenery combined with easy riding. From being squeezed between the cliffs and the river, to cycling through vineyards and orchards, you have it all.

Total distance: Passau - Vienna 335 km (approx. 210 miles) and Vienna - Budapest 340 km (approx. 213 miles) Quaint villages and towns are at regular intervals along the river providing good places to stay and eat. Even without knowledge of German you will have no difficulties finding food and lodging.

The BikeLineGuide provides all necessary information: precise maps, detailed descriptions of the route and sights you'll be seeing, plus a comprehensive list of accommodation.

There is only one trail from Vienna to about 18 kilometers south of Bratislava at Cunovo where it divides. There you have the choice between riding entirely through Hungary or riding on the left side of the Danube through Slovakia. The Slovakian side “ends” at Esztergom and then it is all in Hungary to Budapest regardless whether you choose the left side or right side of the Danube.
If you choose to ride the Slovakian trail there are ample opportunities to cross over to Hungary to visit or even to switch to the trail on the Hungarian side.
Just past Cunovo on the Slovakian trail there is an art museum surrounded on three sides by water, a good place to take a break. This is where over 90% of the water from the Danube is redirected to the man-made lake behind the giant dam at Gabcíkovo.
At Gabcíkovo, you cross over the hydro-electric dam to the left side of the Danube and just after the dam on the right the trail continues onto the levee. From here it is possible to continue on this levee until Radvan (just past Komárno). The guidebook tells you that you need to switch to the road at Medved (here I saw the first stork nest) about 14 km after Gabcíkovo but it is possible to stay on the levee, only leaving it to look for accommodation or a place to get something to eat.
If you are a bird enthusiast then by all means bring your binoculars. On this stretch you are always within sight of the Danube and there are also many ponds that support a wide variety of birdlife. It is possible to swim in the ponds or in the Danube. There are inviting “beaches” on the river along the entire stretch to Budapest. The water is clean and cold but care should be taken about going out too far from shore because of currents.
There are many more places to stay than are listed in the guidebook. The stores are open even on Saturday and Sunday so it is possible to get something to drink or eat even in villages without restaurants.
Just a word about the bike paths on the levees. It is either hard-packed dirt or there is gravel. In places the gravel is deep. It is like driving a car in sand. It is important to keep up a head of steam and a minimum speed. However it was my experience that it was possible to avoid the bad places by either taking the worn path in the grass at the top of the levee or riding on the dirt road with less gravel at the foot of the levee to the right.
About 17 km before Stúrovo/Esztergom you have to get back on the road.
For me, staying in Esztergom and sitting on the terrace of a restaurant or café and watching the sun go down and the Danube flow by is one of the highlights of the trip to Budapest.
From Esztergom to Budapest on the right side of the river just after Visegrad, you take the ferry over to the island Szentendrei Sziget. Unfortunately the traffic on the island has increased since the bridge was built at Tahitótfalu but it is still better than staying on Road 11.
I have never done the bike trail on the left side after Esztergom and have also never talked to anyone who has done it. If anyone has done it or does do it I would love to hear about it.
Shortly after taking the ferry off the island at Szigetmonostor (don’t you love these names!), you arrive in Szetendre which is worth a visit even though it is touristic.
After leaving Szetendre you start your approach to Budapest. I’ve lost the bike path every time I’ve done it. The directions in the guidebook are good but there are so many changes and construction going on that it changes constantly.
If you are going to keep your bike in Budapest and bring it back to Vienna on the train you might consider taking the commuter train in from Bekasmegyer as the guidebook suggests. One of the first things you need to do in Budapest is to arrange your train tickets back to Vienna. Unfortunately all over Europe train service for cyclists has gotten increasingly worse.