In lectures given in 1909 at Columbia, Planck covers basically all of theoretical physics, from thermodynamics to mechanics to special relativity. The lectures are equation heavy, and I often wished for more guidance with them, such as definitions of the symbols. The lectures will be something to go back to as my understanding of the field deepens.
It was cool to read Planck's derivation of h, then realize "hey, that's Planck's constant!", then realize, "oh, that's why they call it Planck's constant .."