The Toome Hill, rising above Old Town, has always been strategic military position. Tartu's original settlement, Tarbatu, was established here in 600AD, and if you trace the hill's outline on a map, you can still see the shape of fortifications built here in the 17th and 18th centuries.
The western part of the hill is clearly dominated by the ruins of the 13th-century cathedral (Toomkirik) that has been decaying since the Livonian War (1558-1583). The sanctuary, which is still in a quite good condition today, accommodates the University’s history museum. Here you can get a broad overview of academic research and teaching in Tartu.
The old observatory of Tartu was constructed in 1811. It was the most modern one in Europe in the 19th century.
References:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.