Prague is a pretty romantic city. If you go there in spring or autumn you will see a very beautiful nature, beautiful architecture. There are a lot of cozy cafes in Prague where you can spend time together, but I advise you to visit the
boat restaurant in prague. It is really a very romantic place. Also, their kitchen will not leave you indifferent. I liked it there very much. I also recommend that you find a guided tour for two. Even an audio tour can be romantic.