FrankfurtRhineMain may be a large region, but it is one where you can get around swiftly and often in an eco-friendly way. Moreover, the parklands, lakes, and hills are all easily accessible.
The network you will probably make the most use of during your stay here is the RMV, the German acronym for the Rhine-Main Transport Authority. This extensive network comprises streetcars, buses, subways and above-ground LRT. The RMV website (www.rmv.de) has multi-lingual information and boasts a trip planner, network maps, and articles on special events in the area and how to get to them.
The system is efficient and reliable. Though not exactly cheap, the cost/benefit ratio for the services is great. A ride from downtown (Konstablerwache) to the airport costs less than € 5 and takes under 30 minutes, for example.