Euromast is an observation tower in Rotterdam, Netherlands, designed by Hugh Maaskant constructed between 1958 and 1960. It was specially built for the 1960 Floriade, and is a listed monument since 2010. The tower is a concrete structure with an internal diameter of 9 m and a wall thickness of 30 cm. For stability it is built on a concrete block of 1,900,000 kg so that the centre of gravity is below ground. It has a “crow’s nest” observation platform 96 m above-ground and a restaurant. Originally 101 m in height it was the tallest building in Rotterdam. It lost this position to the high-rise of Erasmus MC which was completed in 1968, but regained it when the Space Tower was added to the top of the building in 1970, giving an additional 85 m. Euromast is a member of the World Federation of Great Towers. In 2008 and 2009, the tower hosted an extreme sports event which featured BASE jumping.