A forecastle (pronounced “FOH-kuh-sul”) is the forward part of a ship's upper deck, or a raised section at the front of the vessel. On old sailing ships, the forecastle was often where ordinary sailors lived and slept, in cramped quarters below that forward deck.

If you've read adventure stories about life at sea, like Treasure Island or Moby-Dick, the forecastle is where much of the crew's daily life happened: sailors told stories there, mended their clothes, ate their meals, and tried to rest between shifts. The forecastle was their home aboard ship, separate from the officers' quarters toward the stern.

On modern ships, the forecastle (often just called the “fo'c'sle” by sailors) is still the forward part of the ship, though it's now more likely to hold equipment and anchor machinery than sleeping quarters. When you hear someone say they're “going forward to the forecastle,” they mean they're heading to the front of the ship.