Spend Days 1 to 3 as outlined in the other tours. On Day 4, rent a car for a day trip through the scenic Danube Valley centering around Krems and Dürnstein.
You can take the "Austrian Romantic Road" (Route 3) west from Vienna. The route goes along the northern banks of the Danube (which, regrettably, isn't blue as in the waltz). Your first stopover can be at:
At a point 80km (50 miles) west of Vienna, the ancient city of Krems comes into view. This medieval village has a 1,000-year-old history, making it one of the oldest towns in Austria. You can spend at least 2 to 3 hours, wandering its impossibly narrow cobbled lanes, exploring its partially preserved town halls, looking into its mellow courtyards, and going under its arched gateways.
There are more than 700 buildings dating from the 12th to the 19th centuries.
You can have lunch in Krems and even check into a hotel for the night (or else return to Vienna). But save the afternoon for visiting the two attractions listed below.
Take A Break -- A good place to stop for lunch is Restaurant Bacher, serving a first-rate Austrian and international cuisine. The establishment is ideal for motorists, as it offers parking at a point 4km (2 1/2 miles) from the center of Krems. You can also book affordable rooms here if you don't want to drive back to Vienna for the night.
Lying 8km (5 miles) west of Krems, along Route 3, this is the best-known wine town along the Danube. Crowned by the ruins of a fortress, Dürnstein is still girdled by its once-fortified walls. After fighting in the Crusades, Richard the Lion-Hearted was imprisoned here until discovered in 1193 by his faithful minister, Blondel. You can visit the ruins of a castle fortress where he was held prisoner.
In the time remaining in the afternoon, continue along Route 3 to visit:
3. Melk Abbey
At a distance 89km (55 miles) west of Vienna, this abbey is one of the finest baroque structures in the world. The abbey crowns a rocky bluff overlooking the Danube. Its Abbey Church is the highlight of any visit. It is lavishly decorated with gold ornaments, colored marbles, and frescoes.
As mentioned, you can drive back to Krems for the night, or even Vienna. Your call.