We had two great days Prague with accomodation at the Anna Houseboat. My wife and I enjoyed it for our anniversary. The Houseboat is very cozy and the view from the deck on the evening is very romantic.
Daytimes we were in the city and enjoyed the tourists hotspots since the weather was good. We ask about places that we could visit if it was raining and got a recommendation from our host, so they are nice and answered most of our questions in time.
We also bought some food and left it in the fridge and ate it as breakfast.
So overall we had romance, adventure and cost efficiency in two days and recommend it