A mysterious shipwreck hidden beneath the waters of a Finnish fortress raises questions about war, strategy, and a lost vessel. Ancient stone structures revealed at low tide on a remote Taiwanese archipelago hint at a sophisticated and enduring fishing system. Sacred cave temples carved deep into an island off India's coast point to a powerful civilization whose identity has been lost to time. And a windswept Alaskan island scattered with abandoned buildings reveals the haunting remains of a once-thriving military outpost.