This book is another great collection of problems, discussions, and mathematical curiosities from Martin Gardner - and one of his best.
In this book, Martin Gardner has assembled an absorbing discussion on the theoretical aspects and possibility of time travel, including the many paradoxes that may arise; two problem collections to give to try out yourself and give to your friends; two chapters on tangrams and tiling each; along with 15 more chapters on interesting topics such as the melody-making machines, anamorphic art, block packing and more.
Particularly interesting are the chapters "Six Sensational Discoveries" and "Dodgem and Other Simple Games." The former is a collection of six April Fool's jokes he published in April of 1975. The latter is an extensive and occupying discussion of simple games that one can play with friends, along with winning strategies for some and just mathematical theories for others.
I strongly recommend this book for those interested in mathematical curiousities and the likeness. It is especially interesting for children of ages 6-12; they may not understand everything, but certain chapters they will remember and revisit forever!