Favorite thing: Look in the centre at the total new GOETHE GALLERY: as the Sony park in new Berlin-Mid You have an similar architecture, including many shops and the HOTEL ESPLANADE (new also), directly beside the University Library...
... explore the city! lol ;) Just walk along the streets, see some really nice buildings
(e.g. Nollendorfer Hof), visit a museum, go shopping etc.
modern art is allowed! contrary to other 'serious' german cities, here are colors everywhere!!!
Fondest memory: CITYMAP: http://www.jena.de
Favorite thing: The centre is built up new, and has Jugendstil / Gründerzeit (before 1900) also, similar to Berlin-centre!