Ratna Gem Halt is easy to find. The main Entrance is at the Reservoir Road about 700 m far away from the bus station. Tuk tuk transport is about Rs. 100.
Ratnapura bus station
Ratna Gem Halt entrance
If you take the Outer Circular Road, you have to use steps to get to the guest house. Both ways are possible.
References: Ratna Gem Halt is listed in the Lonely Planet Guide
ed. 2014 for Sri Lanka.
Enjoy your stay at Ratna Gem Halt.