By train -  Vienna is a railroad hub, easily accessible from other major European cities. Overnight trains arrive from places like Amsterdam, Strasbourg, Bucharest, Sofia, Belgrade, Berlin, Düsseldorf, Hamburg, Munich, Moscow, Kiev, Milan, Warsaw, Cracow, Prague, Cheb, Rijeka, Koper, Rome and Venice. The day trains from Prague take less than 5 hours, the night train takes less than 8 hours. There are several cheap train offers to and from Vienna, mainly to destinations in Germany and Italy, but also Strasbourg and some other destinations. These all cost €29 for a one-way seater, €39 for a couchette, or €59 for a sleeper. You have to book quite a bit in advance (to Berlin and Hamburg about two months in advance, especially in summer), but it is definitely worth the effort as it takes you right to the center of a city early in the morning (unlike taking the plane) There is a special discounted round-trip ticket you can buy if traveling from Budapest called a "kirandulójegy" or excursion ticket in English. For €29 you can buy a round trip ticket between Budapest and Vienna good for 4 days that will also cover all your local transportation within Zone 100. Since a 3-day transport pass usually costs €12 you're basically getting a round trip ticket for €17! This is an excellent deal especially if you're planning on going back to Budapest. NOTE: There are 2 major train stations, Westbahnhof (West Station) and Südbahnhof (South Station). Südbahnhof does not connect directly to the metro system. The nearest metro station is outside of the station about 400m away. Look for Südtiroler Platz. Many trains from Germany arrive at the Westbahnhof. Trains to Bratislava (only an hour away) usually depart from the Südbahnhof, but occasionally from the Westbahnhof.
By car -  Most Austrian highways ("Autobahn") terminate/originate in Vienna. Unlike Germany, there is a strictly enforced speed limit of 130 km/h on highways (80 km/h on highway sections in Vienna). Within towns it is 50 km/h, and on major roads it is 100 km/h. Also a Highway Toll Sticker (Vignette) is a must! Not having one can be really expensive. Usually they can be purchased at petrol (gas) stations. Drivers in Austria are also required by law to carry certain safety equipment. This includes a reflective vest, first aid kit and traffic warning triangle. It is required to keep your headlights on at all times while driving in Austria.