St. Paul's Cathedral is a Renaissance Church and Sir Christopher Wren's masterpiece, which took 35 years to build. It dominates the North bank of the River Thames. Even though St. Paul's was bombed several times during WWII, it survived because of the determination of the fire brigade.
After the war, the church was renovated and brought back to its former splendor. (Note: The wedding of Lady Diana Spencer and Prince Charles took place here in 1981.) Visible from all over London, the church's dome is patterned after St. Peter's in Rome...this dome is St. Paul's most distinctive feature. It's really a "dome within a dome, supported by a hidden superstructure and crowned with a stone lantern."

When I was inside and looked up, I actually had vertigo! Fortunately, it's possible to climb up for a fantastic view of London. There are three galleries around the dome to experience these views. St. Paul's also has the largest crypt in all of Europe. Appropriately, Sir Christopher Wren is buried here.

Official statement

A Cathedral dedicated to St Paul has overlooked the City of London since 604AD, a constant reminder to this great commercial centre of the importance of the spiritual side of life.
The current Cathedral – the fourth to occupy this site – was designed by the court architect Sir Christopher Wren and built between 1675 and 1710 after its predecessor was destroyed in the Great Fire of London. Its architectural and artistic importance reflect the determination of the five monarchs who oversaw its building that London’s leading church should be as beautiful and imposing as their private palaces.
Since the first service took place here in 1697. Wren's masterpiece has been where people and events of overwhelming importance to the country have been celebrated, mourned and commemorated.
Important services have included the funerals of Lord Nelson, the Duke of Wellington and Sir Winston Churchill; Jubilee celebrations for Queen Victoria; peace services marking the end of the First and Second World Wars; the launch of the Festival of Britain; the Service of Remembrance and Commemoration for the 11th September 2001: the 80th and 100th birthdays of Queen Elizabeth, the Queen Mother; the wedding of Charles, Prince of Wales, to Lady Diana Spencer and, most recently, the thanksgiving services for both the Golden Jubilee and 80th Birthday of Her Majesty the Queen.

The Cathedral is open to sightseers from Monday to Saturday between 8.30 - 16.00 (last admission).