Europe
Danube Cycle Path
The Danube Cycle Path is a very popular European ride that follows the Danube River. The most popular portion crosses Austria.
http://www.danube-cycle-path.com
I did one popular route from Passau, Germany to Vienna, Austria. I flew into the Frankfurt (FRA) airport, took the S Bahn to the central train station (Hauptbahnhof), and took a train to Passau. The second class car was very comfortable and cost about 35 Euro. Many also fly into Munich (MUC).
I used the EuroVelo 6: Danube Cycle Route app to navigate. If you load the maps before you start, it works without data. However, I recommend getting a local data service. My T-Mobile account worked, but the data was worthless.
I rented a bike from Rent a Bike Passau. It is located at the Passau train station. You can reserve online in advance, and I recommend doing so. The shop turned away many people without reservations the morning I picked up my bike. The shop provides an excellent lock and I rented one pannier. The shop doesn't provide a tire kit, tube, or pump, and I didn't need them.
From Passau, take the R1 bike path into Austria. The R1 turns into the Euro 6. Often there are paths on both sides of the river, sometimes multiple paths. I relied on advice from other riders and locals about the route, but there are excellent guide books that describe the options in detail. Crossing the river on the bridges was often a climb, but the ferries were always fun.
There are many restaurants and cafes along the route, so I didn't carry food. I did carry two liters of water, and was able to refill often enough that I never ran dry, for long. There are also many hotels and pensions along the route. I booked rooms for the next day, and never had any problems getting a convenient place.
I dropped my bike off at the Hotel Praterstern. Just walk your bike into the lobby and they will direct you to the large bike storage area in the court yard. You can ride on the bike paths from Praterstrabe near the hotel into central Vienna. The bike paths are a great way to see the sites and many of them are completely separate from traffic. I felt very safe riding in the city. The Hotel Praterstern is also a short walk from the Praterstern Station. From there it is a 20 minute train ride to the airport.