Cape Henlopen is an interesting mix of scattered dunes, and former military fortifications, located on a natural promontory on the Delaware side of the mouth of Delaware Bay, across from Cape May New Jersey. As the gateway to the Delaware River, and the cities of Wilmington, Trenton, and Philadelphia, these two capes were fortified during WWII. At Cape Henlopen the remains from the former Fort Miles are still visible, including buildings, bunkers, and towers. A tall concrete observation tower is open to the public. Another tower is used by river pilots as a ship reporting station, and another is a fire tower. Several gun bunkers also remain, partially buried in the sand. Among the dunes is the Great Dune, the largest sand hill between Cape Hatteras and Cape Cod. Though the dune shrank and eroded in the early 20th century due to the removal of vegetation, the dune was restored to its current height during WWII, when the Army piled sand to hide a gun emplacement. A historic lighthouse on the cape was undermined by coastal erosion, and collapsed into the ocean in 1926. Outside the gate of the park is a pharmaceutical plant (SPI Pharmas Barcroft Company) that makes ingredients for antacids and laxatives, such as Milk of Magnesia, by processing seawater pumped at the site.