Legendary physicist Lev Landau apart from the Physics for Everyone series wrote another book on popular science, with Y. Rumer, it is called What is the theory of relativity?
The book is an attempt to make the readers understand the basic concepts of theory of relativity, both special and general. It serves as an excellent introduction to the subject. In the 64 pages of the book, each page is informative and I think you cannot have a more precise popular introduction to the difficult subject.
The book was published by the Foreign Languages Publishing House in the 1959 and again by Mir in 1970s. It was translated from the Russian by A. Zdornykh and edited by V. Schneierson. Simultaneously it was also published in the west by Basic Books (translation by N. Kemmer) in 1960 and recently Dover has brought a reprint in 2003. All credits to the orginal uploader.
The book contains following sections:
Chapter 1 The Relativity We Are Used To
Chapter 2 Space Is Relative
Chapter 3 The Tragedy Of Light
Chapter 4 Time Is Relative
Chapter 5 Capricious Clocks and Rulers
Chapter 6 Mass