Located in Trentham, Upper Hutt, the Blockhouse was one of several defence buildings in the area. It was built in 1861 due to a perceived threat of Māori attack on Pākehā settlers. An attack that never came.
The American-style military fortification is a rare, surviving example of this style of defensive building in New Zealand.
Colonel Thomas Mould designed the building. The Hutt Battalion of the Wellington Militia occupied it briefly. The two-storey structure is made from timber with shingle infill, to protect it from rifle fire. Loopholes allowed defenders to return fire.
Windows were a later addition, along with metal gratings over the loopholes. The building now also has electric power, security lights, a fire alarm, and a sprinkler system.
Declared a historic building in 1916, Heritage New Zealand managed the building, which is open to the public.
Free on-street parking is on McHardie Street, with bus parking on Fergusson Drive. There is also an accessible drop-off and pick-up point next to the Blockhouse. Heretaunga College shares on-site parking, potentially causing some limitations during school hours.