A Mysterious Universe introduces the fundamental laws of quantum mechanics, theory of relativity, and cosmology to a novice in simple language. This concise book deals with deep issues related to the mysteries of modern physics. Both quantum mechanics and relativity are highly mathematical subjects and are not easily accessible. In 2020, the author wrote a book, Quantum Mechanics for Beginners, with the aim of introducing the fundamentals of quantum theory to someone with elementary knowledge of physics and algebra. Here he goes one step further and introduces these ideas to someone with no prior knowledge of physics and mathematics. In the first part of the book, topics like the wave-particle duality, the probabilistic nature of the measurement, the possibility of multiple universes, and the nature of reality are discussed. In the second part, Einstein's special and general theories of relativity and their amazing and mind-boggling consequences are presented. The impact of the theory of relativity on cosmology is immense. The big bang model of the universe, black holes, and the current hot topics of dark matter and dark energy are explained and discussed. These fields that may hold the key to many unanswered questions about the universe are still evolving.