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.
Steinvikholm Castle is an island fortress built between 1525 to 1532 by Norway's last Catholic archbishop, Olav Engelbrektsson. Steinvikholm castle became the most powerful fortification by the time it was built, and it is the largest construction raised in the Norwegian Middle Ages.
The castle occupies about half of the land on the rocky island. The absence of a spring meant that fresh water had to be brought from the mainland. A wooden bridge served as the only way to the island other than boat. Although the castle design was common across Europe in 1525, its medieval design was becoming obsolete because of the improved siege firepower offered by gunpowder and cannons.
The castle was constructed after Olav Engelbrektsson returned from a meeting with the Pope in Rome, presumably in anticipation of impending military-religious conflict. As Archbishop Engelbrektsson's resistance to the encroachment of Danish rule escalated, first with Frederick I of Denmark and his successor Christian III of Denmark, Steinvikholm Castle and Nidarholm Abbey became the Catholic Church's military strongholds in Norway. In April 1537, the Danish-Norwegian Reformation succeeded in driving the archbishop from the castle into exile in Lier in the Netherlands (now in Belgium), where he died on 7 February 1538. At the castle the archbishop left behind St. Olav's shrine and other treasures from Nidaros Cathedral (Trondheim). The original coffin containing St. Olav's body remained at Steinvikholm until it was returned to Nidaros Cathedral in 1564. Since 1568 St. Olav's grave in Nidaros has been unknown.
From the 17th to 19th century, the island was used as a quarry and some of its masonry was sold and removed from the site. This activity was condoned by the Danish-Norwegian authorities as a way of eliminating a monument to the opposition of the Danish–Norwegian Union.
Steinvikholm fort is owned and operated today by The society for the Preservation of Norwegian Ancient Monuments. The island has been the site of the midnight opera which details the life and struggles of the archbishop. The opera is held in August annually. The opera is organized by Steinvikholm Musikkteater since the beginning in 1993.