Michael Spivak's Calculus on Manifolds caught my eye because of its brevity, and its promise to reveal the fundamental theorem of calculus in arbitrary dimensions. I thought to myself "how hard could it be to read something so short?".
Thus was I lured to an endeavor that has taken far more time than I expected. Over the past couple of years I've put Spivak aside for prolonged periods, but I never put it away entirely. This book has become a constant for me- a source of meditative calm and delight. Similar souls may enjoy my notes and problem solutions:
Chapter 1: Functions on Euclidean Space
Chapter 2: Differentiation
Basic Theorems