Books
Browsing is most useful when there is a finite number of items to sort through. For example, by going to the right section of the books stacks, you can browse books grouped together by the same subject. All math works fall under the general LC class QA. Some rough divisions as follows:
QA5 Dictionaries and encyclopedias
QA95 Mathematical recreations
QA150-255 Algebra
QA241-246 Number Theory
QA273 -280 Probabilities. Mathematical Statistics
QA299.6 - 433 Analysis
QA440 - 699 Geometry. Trigonometry. Topology.
QA801 -939 Analytic Mechanics
Journals
Here are some fun, accessible journals that publish insightful expositions written to inform readers who are new to a topic. Some titles will have current developments in math research, history of math, cultural connections with math and math education and learning. Many book reviews are found here, as well as humor, puzzles and art.
The Mathematical Intelligencer
Print only. Current and bound issues: QA1 .M42