Lectures on General relativity
his personal website : http://preposterousuniverse.com/self.html
Pr. Sean Carroll gave us the authorisarion to install in the web site of " Science without border " a copy of his excellent introduction to General relativity.
Of course, it is not for children. But it is one of the clearest presentations of this pretty hard field. Carrol does not use the classical hierogliphs of mathematical physics ( the well-known "Bourbaki" formalism ! ) . He speaks simply, as an honest physicist and geometer, and sometimes with a good sense of humour.
Students in high level science, take your pen in one hand, aspirin in the other one, and dive into this fascinating litterature.
LINK to the pdf file