Northburgh Castle, also known as Green Castle or Greencastle Castle, is a 13th/14th-century ruin in Greencastle, Ireland. Completed in 1305 by Richard Óg de Burgh, it controlled Lough Foyle and served expansion plans. Edward Bruce captured it in 1316, and it later became an O'Doherty stronghold. The castle features an oval enclosure with a twin-towered gatehouse and a later large tower. Influenced by Edward I, it symbolized a shift from pure military structures to administrative centers. Damaged by cannon fire, the castle is now managed by the Irish government and accessible from the town and shore.