The Schreierstoren, originally part of the medieval city wall of Amsterdam, was built in the 15th century. It was the location from which Henry Hudson set sail on his journey to Northern America. This expedition would lead to the discovery of the island of Manhattan among others. It was built as a defense tower in 1481. It is currently a café.References:
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.