Built by Charles Brooke in 1880 to take control of the Upper Rejang, this wooden fort – built of belian (ironwood) – was renamed in 1925 to honour Ranee Sylvia, wife of Charles Vyner Brooke. The exhibits inside offer a good introduction to the traditional lifestyles of the indigenous groups of the Batang Rejang and include evocative colonial-era photographs. Also on show is the peace jar presented during the historic 1924 peacemaking ceremony between previously warring Iban, Kayan and Kenyah groups.

The museum also devotes space to the story of Domingo 'Mingo' de Rozario, the son of James Brooke's Portuguese Melakan butler and a man described by a contemporary as having 'a burly figure, dark kindly face, utter disregard for personal danger' and the tendency to 'look on life as a huge joke'. Rozario was sent to Kapit and charged with bringing it under the raja's control. He became an authority on Upper Rejang enthnography, describing life in the region in a series of colourful letters and reports.