Amidst the pulsing Old Town Square of the city, the Old Town Hall is the vortex of tourist activity. The several chambers connected inside the Gothic Old Town Hall are venues for exhibitions and events. While the tower of the hall offers terrific views of the historic neighborhood, the underground section is the keeper of Prague's best kept secrets. The real attraction is, however, the Astronomical Clock on the exterior of the hall. Built in the 15th Century and known as Orloj, the clock is a complex set of dials with astronomical details and also positioning of the Sun and Moon. Legend goes that the clockmaker of this unique structure was blinded after its completion and also that the city will face great peril if the clock is neglected and becomes dysfunctional. The figures of twelve apostles were added in 1940 and are designed to move in a particular motion at every hour, just above the clock face. An intriguing and rare monument, the clock is a popular tourist attraction in Old Town.