The second most ancient of Sri Lanka’s kingdoms, Polonnaruwa was first declared the capital city by King Vijayabahu I, who defeated the Chola invaders in 1070 to reunite the country once more under a local leader (wikipedia).
The Ancient City of Polonnaruwa has been declared a World Heritage Site.
This is a very impressive site, better visited on bike as it is quite a long way from one side to the other. The archaeological remains and the temples here are quite impressive and frankly they make a greater impression than Anuradhapura.
The above is a pretty poor picture, but it reflect what is the most impressive in Polonnaruwa: partially standing buildings of more than one levels like than one which give a better impression of what the city could have been.