This book provides a first-hand account of modern cosmology, written by three celebrated astronomers renowned for their excellence in both research and teaching. The central theme of the book, the deep Universe, is approached in three truly complementary ways: as a coherent and smooth theory embracing the evolution of the Universe from its original radiations emerging from the hot Big Bang to the present structures of matter; as a meandering, rough road paved by our observations of stars, galaxies, and clusters; and in terms of how these approaches have been gradually developed and intertwined in the historical process that led to the modern science of cosmology. The book is written for graduate students in astrophysics but is also of interest to professional astronomers and particle physicists.