After liking the Foundation a lot I had to read the only other book by Asimov I own, Zelfs de Goden (The Gods Themselves). This is a standalone book, containing three stories.
The first one takes place on Earth in the future, where a pump is developed that pumps matter from our universe to a parallel universe. This releases a great amount of energy but turns out not to be all as good as expected. In the second story we visit the other universe and the reasons for their pump. The last part takes place on the (colonized) moon and the research into the pumps being done there.
I really liked this book and the stories. The second story was a bit harder to follow because of the strange life forms. All in all a well worked out story that looks at all sides of the argument.