The famous Feynman Lectures on Physics is a physics textbook based on some lectures by Richard P. Feynman, a Nobel laureate who has sometimes been called "The Great Explainer". The lectures were given to undergraduate students at the California Institute of Technology (Caltech), during 1961–1963 and have been a favorite for aspiring physicists ever since.
The three volumes of the book focus on mechanics, radiation, and heat, including relativistic effects (Vol 1), electromagnetism and matter (Vol 2) and quantum mechanics (Vol 3).
In case you didn't know (or forgot) in 2013, Caltech in cooperation with The Feynman Lectures Website made the book freely available, on the web.
As the site says, "Now, anyone with internet access and a web browser can enjoy reading a high quality up-to-date copy of Feynman's legendary lectures. This edition has been designed for ease of reading on devices of any size or shape; text, figures and equations can all be zoomed without degradation.