The charming black and white building known as the Ancient House is one of the best examples of an early Tudor town house in East Anglia. Officially opened as a museum on 11 December 1924, it was inaugurated by the Duchess of Grafton. He joined the Norfolk Museums Service in 1974. The old house was the home of a wealthy merchant who wanted to model his home after the largest houses of the time and was willing to pay the best craftsmen for his construction.

Ancient House houses various spaces and collections that trace the local history of the city and the surrounding area. The Collector's Room is full of treasures and retains many of the features that give an idea of how it might have been used in the past, including the original sloping window.

Inside the museum there is also an authentic 1901 kitchen showing life as it would have been at the Ancient House at the turn of the century, and the Householder's Room examines the lives of four former Ancient House residents: an innkeeper , a plumber, a watchmaker and a museum keeper. The collection includes items that explore Thetford's rich history, from the Celtics, to the Romans and the Vikings, up to the 1960s.