I just read an amazing book called "The Existence of Space and Time" by Ian Hinckfuss (Oxford Press, 1975). Philosophy of physics behind space and time. It is also somewhat covertly about relativity. Very short, very readable (based on lectures given), super clear. It also has very nice bibliographies at the end of each chapter. If you are about to jump into Max Jammer's "Concepts of Space" and/or Reichenbach's "Philosophy of Space and Time" this would be a good primer. Maybe this isn't much of a review but I just felt like this is a lost gem. In particular the very first subsection in the first chapter "What is space?" poses the issue most admirably.