Searcóid: Elements of Abstract Analysis. I loved this book as an undergraduate, for many reasons, but mainly because it gave me an idea of the unity of mathematics. It starts from the axioms of set theory and takes you  all the way to C*-algebras and the Gelfand-Naimark theorem. Here's the [Google Books page][1].


  [1]: https://books.google.com/books?id=c3ChND-I42wC&dq=%22elements+of+abstract+analysis%22&source=gbs_navlinks_s