Hi guys. I finished working through D'Inverno's "Introducing Einstein's Relativity" and Schutz's "A First Course in General Relativity" and some of Carroll's "Spacetime and Geometry" but I don't really feel like I learned most of what is out there. I also feel that before I can tackle Wald I need to read up on a proper introductory differential geometry book. If anyone could recommended me one that would be great. Thanks in advance.