EXCLUSIVE: Alec Baldwin will be the on-air host of National Geographic Channel‘s Friday primetime programming block Night Of Exploration, which features programming that celebrates the spirit of exploration and groundbreaking discoveries. His duties begin June 14 with Crossing The Ice, which follows two Australians as they attempt to become the first to journey from the edge of Antarctica to the South Pole and back unassisted. The network also has unveiled premiere dates for five new summer series, including the newly announced The Castle (TBA August), a spinoff from Nat Geo’s popular series Doomsday Preppers, and Inside Secret America (July 10 at 10 PM). The Castle, from Doomsday Preppers producer Sharp Entertainment, features American prepper Brent Bruns who builds a castle deep in the South Carolina woods that will serve as a bunker in case an electromagnetic burst results in a massive power outage. On Inside Secret America, a Nat Geo TV production, investigative journalists Mariana van Zeller and Darren Foster go inside the nation’s underground networks to the heart of America’s most controversial issues. The two series join previously announced new series Battleground Afghanistan (July 1, 9 PM), Eyewitness War (July 1, 10 PM & 10:30 PM), and Inside The American Mob (July 28, 9 PM), as well as returning shows Doomsday Preppers, Ultimate Survival Alaska, Life Below Zero, Taboo USA and Diggers.