Flying options
Jena can be reached by train (in reasonable time) from the following airports:

Frankfurt am Main (FRA): approximately 3 hours, to “Jena West” via Erfurt or Weimar.
Berlin-Schönefeld (SXF) or Berlin-Tegel (TXL): approximately 3 hours, there are direct trains to “Jena Paradies” from train stations in Berlin.
Leipzig/Halle (LEJ): approximately 1 hour and 30 minutes, to “Jena Paradies” via Leipzig or Halle.
Nürnberg (NUE): approximately 2 hours and 30 minutes, there are direct trains from Nürnberg Hbf (main station) to “Jena Paradies”.
München Franz Josef Strauß (MUC): approximately 5 hours, to “Jena Paradies” via München Hbf.

Arriving by train
If you are coming from the south (e.g., München) or the north (e.g., Berlin), look for train connections to “Jena Paradies”. If you are coming from the west (e.g., Frankfurt am Main) look for train connections to “Jena West”.
Train schedules can be found at the Deutsche Bahn web page.

Arriving by car
Autobahn (motorway) A4 Frankfurt am Main-Dresden passes through Jena, from this motorway you can take either “Jena-Zentrum” or “Jena-Göschwitz” exit. The intersection of motorways A4 and A9 (Rostock-München), “Hermsdorfer Kreuz”, is not far from Jena. In order to reach Jena from A9, one has to drive in the direction of Frankfurt am Main at the “Hermsdorfer Kreuz” junction.