It’s been 15 painful years, and the wreckage from the fallen World Trade Center has finally settled into something concrete: a pair of sunken pools and New York’s tallest building. No small feat. But ground zero has turned into something so much more than a memorial. It’s also a working mini-city, complete with an elaborate transit hub that looks poised to soar, a shopping and dining destination and a tourist attraction. On the 15th anniversary of 9/11, experience a rare and intimate 360-degree video tour of Lower Manhattan.