Get down on Unawatuna Railway Station and walk to the right after crossing the road, on the path which is by the railway tracks. After 50 meters you'll see a board on the right mentioning the Rockstel Unawatuna and walk on that path and you'll see the hostel on your left.
And if you're coming on a vehicle from Eramudugaha Junction (which has Buddhist statue) continue on the Hennatigala Road. Pass the railway tracks and continue straight on the road. On the right you'll see Honda Service station after that take right on the concrete road and follow up the rockstel Signboards and at the end of the road you'll find The Rockstel Unawatuna.