Your question seems quite broad, but I assume you are asking how to make an interesting story if you are restricted to the one location?
If it were me, I'd look for an older property with some character and make the story revolve around the house itself. Perhaps the man acquires the property knowing very little about it (inherited perhaps) and discovers the place holds a number of mysteries that are revealed over the course of the story, the nymph being one of them. It could be that the nymph is bound by the property or something like that, and cannot leave unless the man discovers a way to free her. He sets out to do just that by piecing together clues, using things he finds in the house from the previous keeper. This would also give you the angle for the nymph to fall for him.
Most importantly, whichever way you go with it, make the characters as interesting as possible, that's where the heart of your story lies. Introduce conflict throughout, both in their exchanges and their personalities in general, in order to make them opposing forces (and allies at the same time).