Westminster Abbey was consecrated on 28 December 1065.
There has been a church on the site since the late 8th century, when a small community of monks formed a monastery there; it's possible the site dates back as far as the early seventh century, to the time of the first Christian king of the Saxons, Saberht. King Edward I (later known as Edward the Confessor) decided to expand the Benedictine monastery around 1040, and ordered construction of a new stone church in honor of Saint Peter. The church became known as "west minster" to distinguish it from Saint Paul's Cathedral, which was the "east minster." By the time the church was consecrated 25 years later, Edward was too ill to attend, and he died a few weeks later. He was buried in front of the high altar.
Most of the original abbey was lost when Henry III decided to remodel it in the new Gothic style during the 13th century.
Beginning with William the Conqueror in 1066, Westminster Abbey has witnessed all but two coronations. It has hosted 16 royal weddings, and houses the remains of 17 (now 18?) monarchs. It is also the final resting place of many notable writers, poets, scientists, and politicians.
They still hold special services at the abbey, despite all the tourist traffic; the only time a pope has visited was Benedict in 2010.
Who's your favorite personage monumented there?