Gatehouse

n. lodge, house next to the entrance of an estate or park

A gatehouse is a feature of European castles, manor houses and mansions. Originally a gatehouse was a fortified structure built over the gateway to a city or castle. In architectural terminology, a gatehouse is a building, enclosing or accompanying a gateway for a castle, manor house, or similar buildings of importance.
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Noun
1. a house built at a gateway; usually the gatekeeper's residence
(hypernym) house
(hyponym) lodge

(n.)
A house connected or associated with a gate.
  

A building forming the gate of a castle , generally encompassing a narrow passageway with several gates. Often the gatehouses were fitted with arrow-slits, murder-holes, or other ingenious defensive devices designed to wreck havoc upon the besiegers as they attempted to storm the gates. Some gatehouses held lodgings for guards with rooms for officers above and prisoners below.