Books of interesting mathematics aimed at mathematicians

I'm currently in my third year of an undergraduate degree, mainly doing courses in abstract algebra. I'm enjoying my degree, but every so often when I'm swamped with difficult proofs, I feel like I need some extra inspiration to give myself more mathematical energy and remind me why I got interested in maths in the first place - otherwise I wear myself out. I do things like watching videos on numberphile, but I feel like this is aimed at a much lower level than I'm at.

My question: What is a good resource that features advanced mathematics and isn't shy about going quite deep, but is still fairly recreational in its nature? I don't really care what form this resource takes, it could be blogs, books, videos etc.

Any help would be greatly appreciated.

The Princeton Companion to Mathematics by Tim Gowers et al. is an astounding work. It has an entry for almost any mathematical topic you can think of, and you can get an feel for the flavor of all the areas of mathematics via the typically lucid, not-extremely-technical (for an undergraduate with some mathematical background, anyway) expository articles on the major topics. It's also full of biographies of mathematicians, historical exposition, and essays by leading mathematicians on doing and loving mathematics. Highly recommended.

My personal favorite actual math book in the context of your question is Silverman and Tate "Rational Points on Elliptic Curves."

Another excellent math-type book is Havil "Gamma Exploring Euler's Constant."

On a less technical level, here is a list from the Cambridge Math Dept. with an excellent selection:

http://www.maths.cam.ac.uk/undergrad/admissions/readinglist.pdf

I really like John Conway's Symmetries of Things, which you'll be in a great position to appreciate, taking abstract algebra. It's divided into three sections, the first of which is nice and easy, and things escalate quickly. It's an odd, but good, mix between pop math and a classification of symmetry groups in small dimensions (cylinders, the plane, $3$- and a bit of $4$-space).

Journey through Genius by William Dunham is a fun book that's much more laid back, but still full of very good mathematics, and the mathematicians known for each topic.

Finally, for a very laid back book, I've come across two biographies of Paul Erdös. I know one is called The Man Who Loved Only Numbers by Paul Hoffman. I can't remember the other, but they were both good, even after I'd read one, so either should be a fun read. I don't think you'll learn much math here, although you may learn of some theorems/topics.

Following books may help you: 1.One,Two,Three....Infinity- by George Gamow

2.Fun and fundamentals of Mathematics- by Jayant V Narlikar and Mangala Narlikar.

These books take you through basic concepts of mathematics to the complex ones unveiling the beauty of mathematics.