High Quality Content by WIKIPEDIA articles! The Monmouth Regimental Museum is located on Castle Hill in Monmouth, Monmouthshire, Wales. The museum is in a wing of Great Castle House, a listed building on the Monmouth Heritage Trail. The focus of most of the museum`s exhibits is the most senior regiment in the British Territorial Army, the Royal Monmouthshire Royal Engineers (Militia). Great Castle House is home to the Royal Monmouthshire Royal Engineers, and the museum maintains the records of the regiment.