I love this one. It is one of the most stimulating books on geometry that I have ever read: it is strikingly innovative and really enjoyable (also, it does not require a particularly advanced background).
From the book description:
New Horizons in Geometry represents the fruits of 15 years of work in
geometry by a remarkable team of prize-winning authors—Tom Apostol and
Mamikon Mnatsakanian. It serves as a capstone to an amazing
collaboration. Apostol and Mamikon provide fresh and powerful insights
into geometry that requires only a modest background in mathematics.
Using new and intuitively rich methods, they give beautifully
illustrated proofs of results, the majority of which are new, and
frequently develop extensions of familiar theorems that are often
surprising and sometimes astounding. It is mathematical exposition of
the highest order.
The hundreds of full color illustrations by Mamikon are visually
enticing and provide great motivation to read further and savor the
wonderful results. Lengths, areas, and volumes of curves, surfaces,
and solids are explored from a visually captivating perspective. It is
an understatement to say that Apostol and Mamikon have breathed new
life into geometry.