The bus is by far the most flexible and affordable way of getting to Heidelberg and costs ~7 Euro per person.
It runs every 20 minutes and takes between 1 hour to 1 hour 20 minutes depending on the coach you catch. The company which operates the service is called Flixbus.
You can buy the tickets online / via the app (Route: Frankfurt Airport (P36, Terminal 1) to Heidelberg central train station). Note that :
You can also buy the ticket directly with the driver (the price might be higher though).
Provided you have a valid ticket, the steps to get from the airport to Heidelberg are:
Go to the Flixbus terminal at the airport and to bus stop P36.
To get there, exit concourse C of Terminal 1 on the arrival level and keep to the right. Check out the walking route. If you arrive at Terminal 2 take the SkyLine to Terminal 1.
Once on the bus, please pay attention to when you reach Heidelberg (the bus is most likely scheduled for further stops down the line). You will want to get off at Heidelberg Hauptbahnhof (Heidelberg Central Station).
From the central station, you can either use further public transportation to reach your destination or a taxi (note that they only take cash). There is a tourist information in front of the train station (marked with a large letter “i”). If you have any issues at all, please call us!
Note that you could, in principle, also take a train to Heidelberg, but you would have to change either in Mannheim or in Frankfurt City and it is likely to be more expensive.