A few facts you might not know about one of London's most recognisable landmarks.
1. It took more than 30 years to build
The task of designing a new St Paul's Cathedral was officially assigned to Sir Christopher Wren on 30 July 1669.
The "topping out" of the cathedral (when the final stone was placed on the lantern) took place on 26 October 1708, performed by Wren's son Christopher Jr and the son of one of the masons. The cathedral was declared officially complete by Parliament on 25 December 1711 — what an awesome Christmas present.
In reality, construction continued for several years after that, with the statues on the roof added in the 1720s. By 1716 the total costs amounted to £1,095,556 (£148 million in today's money — and quite a steal when you think how much was spent on the Garden Bridge without it actually being built).
2. It was the tallest building in London for over 250 years
At 365 feet (111 m) high, St Paul's was the tallest building in London from 1710 to 1965.
It was overtaken by the BT Tower in 1962, which was topped out in 1964 and officially opened in 1965.
Today, St Paul's stands down in about 50th place in a list of London's tallest buildings. How the mighty have fallen.
3. It's the second biggest church in the UK
St Paul's is the second-largest church building by area in the United Kingdom. After? Liverpool Cathedral.
4. The bells of St Paul's: two more 'second biggest'
Cast in 1878, the 12-change ringing bells hanging in the north west tower of St Paul's form the second largest ring of bells in the world.
St Paul's is also home to the second largest bell ever cast in the British Isles: Great Paul, which weighs 16-and-a-half tons. (The largest bell cast in the UK was the one used in the 2012 Olympic Games Opening Ceremony.)
Sadly, Great Paul has not sounded for several years because of a broken chiming mechanism. You can see a video of it ringing here, from 2010:
There are also three clock bells. The largest, Great Tom weighs more than five tons. As well as chiming the hours, Great Tom is tolled on the death of various important people including members of the royal family, the Archbishop of Canterbury, the Bishop of London, the Dean of St Paul's or the Lord Mayor of London.
5. It's had its fair share of celebrity visitors
Services held at St Paul's have included the funerals of Lord Nelson, the Duke of Wellington, Sir Winston Churchill and Margaret Thatcher; jubilee celebrations for Queen Victoria; peace services marking the end of the first and second world wars; the wedding of Charles, Prince of Wales and Lady Diana Spencer; the launch of the Festival of Britain; and the thanksgiving services for the Silver, Golden and Diamond Jubilees and the 80th and 90th birthdays of Elizabeth II.
6. It survived the Blitz... but only just
The image of St Paul's Cathedral, standing proud and unscathed during the Blitz, while London burns around it is a powerful one.
In fact, the cathedral was bombed during the war — a lot. Which makes it even more remarkable that St Paul's survived.
On 12 September 1940, a time-delayed bomb that struck the cathedral was successfully defused by a bomb disposal detachment of Royal Engineers. Had this bomb detonated, it would have totally destroyed the cathedral.
The cathedral was also hit by bombs on 10 October 1940 and 17 April 1941. The first destroyed the high altar, while the second hit the north transept and left a hole in the floor above the crypt. The force of the latter bomb is believed to have been sufficient to shift the entire dome laterally, by a tiny distance.
If you head to the west end of the nave today, you can see a large white diamond-shaped floor tile: a memorial to the volunteers of the St Paul's Watch, the team responsible for defending the cathedral from attack during the second world war.
7. You can see Wren's preferred designs inside
The Great Model was Wren's favourite design; he thought it a reflection of Renaissance beauty.
It's housed within the cathedral itself, in the Trophy Room.
8. There's a painting inside that's been around the world
You can find Light Of The World, by Victorian artist William Holman Hunt in the Chapel of Saints Erkenwald and Ethelburga at the end of the north transept.
The painting shows Christ standing in a dark wood, holding a lantern, and knocking at an overgrown door with no handle.
It's sometimes known as 'a sermon in a frame' (Holman Hunt didn't really do subtlety) and has certainly been around a bit.
Bought by shipowner and social reformer Charles Booth in around 1908, the painting went on a world tour between 1915 and 1917, and drew huge crowds. Its thought some two million people saw the picture; there are claims four-fifths of Australia's population viewed it.
9. It has the largest crypt of any cathedral in Europe
The crypt of St Paul's actually serves a structural purpose.
Although it is extensive, half the space of the crypt is taken up by massive piers which spread the weight of the much slimmer piers of the church above.
While the towers and domes of most cathedrals are supported on four piers, Wren designed the dome of St Paul's to be supported on eight, achieving a broader distribution of weight at the level of the foundations.
10. It contains a 'second hand' sarcophagus
Look out for the tomb of Horatio Nelson in the crypt, striking with its shiny, black marble sarcophagus.
The sarcophagus is actually one of the oldest things inside the cathedral; it was made in the 1520s for Cardinal Wolsey, Henry VIII's Lord Chancellor. When Henry and Wolsey fell out over Henry's divorce plans, the sarcophagus was never used.
Nearly 300 years later, it was presented to the Admiralty by George III as a tribute to the naval hero, Lord Nelson.
11. Hidden figures: there's even a space rocket inside
Head to the American Memorial Chapel in the east end of the cathedral, and you can spot an unusual carving: a slender space rocket, in amongst the North American symbols, emblems, native plants, flowers and birds.
It's a nod to the achievements of the US in space exploration in the 1950s.
12. St Paul's Cathedral: film star
St Paul's has been used in loads of films and TV shows.
You can see the famous church in Lawrence of Arabia; The Madness of King George; Sherlock Holmes; Star Trek Into Darkness; Thor: The Dark World; and London Has Fallen. It has twice featured in Doctor Who.
And the Geometric Staircase in the south-west bell tower was used to brilliant effect as the route to the Divination Classroom in Harry Potter and the Prisoner of Azkaban.
But while the Cathedral gets a good name check in Mary Poppins, another look at this clip will instantly tell you this wasn't filmed anywhere near our London landmark, but on a set in the Walt Disney Studios in Burbank, California.
Tissues at the ready:
13. There are still bits of the cathedral that remain unexplored
It's hard to believe, but the St Paul's Cathedral building is just so vast, and so complex, that there are still areas that remain unexplored by the people that work there.
Watch this video to find out more:
With thanks to guidelondon.org.uk for some excellent tips.