In my Sri Lanka itinerary I particularly enjoyed this site perched on the Mihintale hills, on the mountain of Mahinda. To get there you have to climb the 1,840 stone steps with groups of local pilgrims who flock from all over the island to visit these places. It is also there that Mahinda, a disciple of Buddha and from where the mountain gets its name, supposedly came to hear the words of his master. I particularly enjoyed ascending with all the local population (which requires a little effort under the blistering heat if you leave too late) and the majesty of the site once you arrive at the summit. The view is unbeatable and there is a soothing and magical atmosphere over the site.
Caution: as a Westerner, you can also yourself be seen as an attraction for the local youths - often more interesting than the site itself! Adolescents for which this site is part of their Sunday routine can follow you and photograph you on their mobile phones. Don't forget to always dress appropriately.