gatehouse

/ˈɡeɪtˌhaʊs/
noun
  1. A small building at the entrance to a large property, such as a castle, park, or estate, often used as a guardhouse or residence for a gatekeeper.
    • The guard checked our passes from the window of the gatehouse.
    • The old stone gatehouse still stands at the entrance to the manor.
    • We rented a cottage that was once the gatehouse of a Victorian estate.