Try and get here early after lunch (or first thing in the morning) to have the eerie sensation of being alone in some of the longest and deepest tin mines in the world. The cold tunnels are quite a clammy and claustrophobic experience, and you'll need to watch your head, but there are fascinating insights, such as the mine at the end that was secretly robbed of its ore by out-of-work miners after the mine had shut.
Bus 500 from the local bus station runs to the town of Sungai Lembing (RM4, every 20 to 30 minutes, one hour); from the bus drop-off on the main road, the mines are around a 1km walk up the winding hill road just to the right of the museum as you face it.