Frankfurt Airport is also known as Frankfurt International Airport or the Rhine-Main Airport and is by far the largest airport in Germany. With direct connections to the whole world, it is one of the world's major aviation hubs. The airport area is located  in the southwest of the city, in the Frankfurt Stadtwald.

Conveniently, the airport has its own train station which is connected to the national and local commuter railway system. If you take an S-Bahn right after you arrive, you can reach the centre in 15 minutes. The S-Bahn runs in 15-minute intervals, thus it is never a long wait.
If you like it to be a bit more more comfortable, it is easy to take a taxi into down-town, the ride costs about 25, - euros.

Tip: Book Austrian redcab online up to two days before departure for your transfer in Frankfurt.