The bishop castle of Haapsalu was built in the 13th century. It was the main residence of the Bishop of Läänemaa. The Läänemaa bishopric was created as a state of the Holy Roman Empire on 1 October 1228.
Construction, widening and reconstruction of the stronghold went on throughout several centuries, with the architecture changing according to the development of weapons. The stronghold achieved its final dimensions under the reign of Bishop Johannes IV Kievel (1515–1527). The western side of the castle houses a 29-metre watchtower dating from the 13th century, later used as a bell tower. The walls were later raised to 15 metres. The inner trenches and blindages, which were built for cannons and as a shelter from bombing, date back to the Livonian War (1558–1582), but it was during this war that the stronghold was severely damaged. The walls of the small castle and the outer fortification were left partly destroyed.
In the 17th century, the castle was no longer used as a defensive building by the Swedes who now ruled the Swedish Estonian Province. In the course of the Great Northern War in 1710, Estonia fell under Russian rule and the walls were partially demolished at the command of the Peter I of Russia, turning the castle in effect into ruins.
The Cathedral of Haapsalu is attached to the castle. It was the official chair of the Bishop, was situated and where the Chapter of the Bishopric worked. It is the biggest single-naved church in the Baltic countries, with its 15.5-metre-high domical vaults and an area of 425 m2. The Dome church was probably built in the 1260s, following the style of the Cistercian Order. The round baptism chapel on the eastern side of the church was built in the 14th or 15th century and is the site of a famous legend. On moonlight August nights the shape of a Lady in White appears on the inside wall of the chapel as the moon shines through the chapel window. This Lady is said to have been a woman who was in love with the abbot and entered the castle against his orders, therefore having been walled in there alive as a punishment. The church has been restored and it is again in active use by the local congregation of the Estonian Lutheran Church since 1990.
The city walls of Avila were built in the 11th century to protect the citizens from the Moors. They have been well maintained throughout the centuries and are now a major tourist attraction as well as a UNESCO World Heritage Site. Visitors can walk around about half of the length of the walls.
The layout of the city is an even quadrilateral with a perimeter of 2,516 m. Its walls, which consist in part of stones already used in earlier constructions, have an average thickness of 3 m. Access to the city is afforded by nine gates of different periods; twin 20 m high towers, linked by a semi-circular arch, flank the oldest ones, Puerta de San Vicente and Puerta del Alcázar.