William’s half-brother, Thomas Becket, a motte you can still scramble. Berkhamsted Castle is English Heritage, free to enter, and the first thing children should see when they get off the train. Combine with the canal and a High Street bun.
The essential Dacorum landscape. Start at the monument or at Aldbury, pick a colour of mud, and accept that summer Saturdays are communal. Bluebells in spring are famous for a reason; so are the car parks that fill by 10am.