Tartu Old Observatory

Between 1816 and 1855 Friedrich Georg Wilhelm Struve measured a chain of triangulation points running from the Arctic coast of Norway to the Black Sea - over 2,800 kilometres - to work out the exact size and shape of the Earth. The chain is inscribed as the Struve Geodetic Arc, a World Heritage Site spread across ten countries, and its first point and scientific home is this small observatory on Toomemägi in Tartu.

What you actually see

A neat neoclassical observatory building from 1810 with its dome and observation slit, restored as a museum of astronomy and geodesy. Inside are the instruments of the era, including the famous Fraunhofer refractor - in its day the largest achromatic telescope in the world - and the story of how the arc was measured with rods, angles and enormous patience.

The Struve point itself is marked in the building, and the terrace gives a view over the old town below.

When to go

• Any season - it is a compact indoor museum.
• Combine with Toomemägi - the cathedral ruins, the angel's bridge and the university museum are all on the same hill.

Honest expectations

This is a small, quiet museum about measurement, and its appeal depends on caring about the story. For anyone interested in the history of science it is one of the most significant buildings in the Baltics; for anyone else it is a pleasant half hour.

Labelling is good in English, but the exhibition is instruments and documents rather than interactive displays.

Nearby

Tartu old town is directly below the hill. The university's main building and the Estonian National Museum round out the same day.