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 (30 ft) and a wall thickness of 30 cm (12 in). For stability it is built on a concrete block of 1,900,000 kg (4,200,000 lb) so that the centre of gravity is below ground. It has a "crow's nest" observation platform 96 m (315 ft) above-ground and a restaurant. Originally 101 m (331 ft) in height it was the tallest building in Rotterdam. It lost this position for a while, but regained it when the Space Tower was added to the top of the building in 1970, giving an additional 85 m (279 ft). Euromast is a member of the World Federation of Great Towers.