Okay kiddo, let me explain what a gatehouse at Bonds Mill is like you are five years old.
A gatehouse is like a small house that is built beside the entrance of a bigger property, like a castle or a big mansion. It is like a little house that guards the entrance to the bigger place.
At Bonds Mill, there is also a big property and it has a gatehouse too. It was built a long time ago and it used to be a place where people would come to check who was coming in and who was going out.
The gatehouse would have a gate that would swing open and close to let people in and out. There were also little windows where someone could look out to see who was coming.
But now, the gatehouse is not being used for that anymore, it's just there to remind us of the past and how people used to live long ago. So, it's like a really cool and interesting building to visit and see what life was like back then.