Thank you David! The lower right 1964 stamp shows the Vatadage of Medirigiriya. 'Rediscovered' in 1897 by the British Commissioner to the Ceylon Civil Service, HCP Bell. He kicked off restorations, and by 1945 Medirigiriya opened to the public. 
The 1950 version of the same vatadage view. Now, due to encroachment, less than half of the original 600 acres and structures set aside for the preservation of the Medirigirriya archaeological landscape exist.