Intuitive

• https://gravityandlevity.wordpress.com/2010/12/07/feynmans-ratchet-and-the-perpetual-motion-gambling-scheme/

Concrete

Recommended Lecture Notes:

• http://www.inference.org.uk/sanjoy/teaching/thermo/

Recommended Papers:

• Gibbs vs Boltzmann Entropies by E. T. Jaynes; especially the section ""Intuitive meaning of the second law".

Abstract

Recommended Papers:

• On Geometry of Phenomenological Thermodynamics by Jerzy Kocik

Why is it interesting?

“….[classical thermodynamics] is the only physical theory of universal content which I am convinced will never be overthrown, within the framework of applicability of its basic concepts.“

Einstein

“The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell’s equations — then so much the worse for Maxwell’s equations. If it is found to be contradicted by observation — well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation.“

Eddington

“If physical theories were people, thermodynamics would be the village witch,” the physicist Lídia del Rio and co-authors wrote last year in Journal of Physics A. “The other theories find her somewhat odd, somehow different in nature from the rest, yet everyone comes to her for advice, and no one dares to contradict her.”

https://www.quantamagazine.org/the-quantum-thermodynamics-revolution-20170502/

FAQ

What is the conceptual difference between Gibbs and Boltzmann entropies?

See https://physics.stackexchange.com/questions/141321/what-is-the-conceptual-difference-between-gibbs-and-boltzmann-entropies and also Gibbs vs Boltzmann Entropies by E. T. Jaynes;