Caves. This seems to be the great pride of Sarawak (among many others) and the area had the biggest caves in the world.
I liked Niah Caves the most, since it proved human inhabitation during time, beginning with the impressive discovery of the so-called 'Deep Skull' dated to 40.000 BC.: The skull hereby getting the status of the oldest human discovery in Borneo.
Beautiful red painting on the walls of the caves was another good reason for my preference over the caves, even though these paintings are not yet to be dated (however :ooooooold; would be a good enough dating for most tourists).