For those seeking a deeper understanding of mathematics, particularly in calculus and geometry, several books stand out for their theoretical insights rather than problem-solving focus. Notable recommendations include "Mathematics from the Birth of Numbers" by John Gullberg and "Mathematics and Its History" by John Stillwell. Additional titles that capture the elegance of mathematics include "The Art of Mathematics: Coffee Time in Memphis" by Bela Bollobás, "A Mathematician's Lament" by Paul Lockhart, and "The Joy of x: A Guided Tour of Math, from One to Infinity" by Steven Strogatz. Works by Ian Stewart, Roger Penrose, and Keith Devlin are also suggested for their blend of theory and practical application, appealing to readers interested in the beauty of mathematical concepts akin to the way "Hyperspace" and "The Elegant Universe" explore theoretical physics.