Happy Tuesday. The world is full of mysteries—and even the smallest of them can inspire wonder. What's actually inside this concrete book, for example? Or what goes into a magician's repertoire? Answers and more below.  The Mystery of the Concrete Book This unusual tome, titled Betonbuch (Concrete Book), was “published” in Zurich, Switzerland, in 1971 by experimental artist Wolf Vostell. It is one of 100 copies he created by, Vostell explained at the time, encasing a 26-page booklet in concrete. Or so it seems. Is there actually a booklet inside the concrete? Or just an artist’s prank? Simply cracking the work open to discover the truth isn’t an option, so to science we must turn! READ MORE → Places of the Day Bridge of Sighs Chester, England Constructed during the late 1700s, prisoners who had been condemned to death crossed this bridge from the city jail to the former Chapel of St John for their last rites. READ MORE → Fort Gorges Portland, Maine By the time this fort was completed at the end of the Civil War, it was completely obsolete. After a failed modernization attempt in the 1870s, it sat empty and unused for nearly 100 years. READ MORE → FBI Spy House Washington, D.C. A painfully obvious spy house sits right across the street from the Russian Embassy.The house’s owner was listed as “FBI” in public records, and its inhabitant’s occupation as “Clerk - really a spy.” READ MORE → The Explorer’s Guide to L.A. Sponsored by Los Angeles Tourism  Dreaming of Los Angeles? Find your next adventure in this amazing city using our Explorer’s Guide to L.A., a unique interactive map that features fascinating finds from downtown to the beach cities. Pick any of the five neighborhoods listed to discover something wondrous just off the beaten path that’ll be sure to make your next trip to L.A. unforgettable. READ MORE → Alaska’s Famously Chunky Bears For many viewers, after a summer of salmon-catching, bruising brawls, and rather perfunctory courtship, autumn’s highlight is voting in Fat Bear Week. The fatter the bear, the better its chances of surviving the long, lean months of an Alaskan winter, nestled snugly in its den. Fat Bear Week kicks off on September 28, so tune in tomorrow—but until then, join us in learning how biologists are figuring out exactly how big these bears can get. READ MORE → 4 Libraries With Culinary Treasures For most of human history, there weren’t many books about food. But the 19th century changed that, as printing technology and, more importantly, increased literacy created a veritable cookbook boom, creating valuable windows into everything from culture and community to religion and the environment. Here are four stellar archives within the United States alone. READ MORE → Building Bridges At 32 years of age, Hashiwokakero is one of the older puzzles in Japan’s Puzzle Communication Nikoli, the most influential puzzle publication in history. Though it is grid-based, there is no actual grid present, only circles containing numbers. Your task is to draw connections between the circles. Each island (circle with a number) is connected to the others by one or more bridges. The number denotes how many bridges serve that island. Good luck!