Fantastic museum. The very unique and interesting history of Sarawak, with a large focus on James Brooke (the "White Raja") and his descendants, is well presented and explained. The fort is well kept and and great sight, but the real interest lies inside with the clearly articulated and excellently presented exhibits.
In terms of accessibility, note that the majority of the artifacts and information are up a spiral staircase or two. Climb the third staircase for the view of the city. Also, currently quite difficult to get to the entrance from the waterfront but it looks like a new entrance is being built which I was told would be finished by Summer 2018. I imagine one could then catch a ferry from the waterfront to this new entrance. 20RM per person felt very reasonable. More