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Estonia UNESCO world heritage sites

Harju district [capital = Tallinn]

Historic Centre of Tallinn see detail
It developed as a major centre of the Hanseatic League, and its wealth is demonstrated by the opulence of the public buildings (the churches in particular) and the domestic architecture of the merchants' houses, which have survived to a remarkable degree despite the ravages of fire and war in the intervening centuries.

Laane-Viru district [capital Rakvere]

Struve Geodetic Arc in Voivere + Simuna
The Struve Arc is a chain of survey triangulations stretching from Hammerfest in Norway to the Black Sea, through 10 countries and over 2,820 km. These are points of a survey, carried out between 1816 and 1855 by the astronomer Friedrich Georg Wilhelm Struve, which represented the first accurate measuring of a long segment of a meridian.

Tartu district [capital = Tartu]

Struve Geodetic Arc in Tartu
See above.