Westminster Abbey is a large church in the Gothic style in London, England. Edward the Confessor built an abbey here (an abbey is a place for monks or nuns to live and pray) in 1050 AD, in the Romanesque style.
William the Conqueror was crowned in the Abbey, and so have been all English kings and queens since his time right up to now. By 1245, however, that old Romanesque church seemed hopelessly old-fashioned, and the kings of England were richer (maybe thanks to the Medieval Warm Period), so Henry III decided to tear it down and build a much bigger new church in the Gothic style. But they got a little too ambitious and ran out of money. The facade (the front) of Westminster Abbey, though, wasn't actually finished until the 1400s AD. Because of this, it is in a Late Gothic style which is much more vertical. Most of the lines go up-and-down and not across. (The two towers were not built until the 1700s)
Unlike the doors of Italian or French cathedrals, the doors of Westminster Abbey are relatively plain, with beautiful lacy garlands but no statues - they don't tell a story.
Inside, the main nave of Westminster Abbey rises in three storeys - one big pointed (Gothic) arch at the bottom, then a blind (false) gallery, and above that a big glass window to let in the light. Thin colonnettes attached to the wall rise straight up from the floor to the ceiling to make the ceiling seem as high as possible, as if the whole building were soaring up to the sky, trying to leap right up off the ground to Heaven.
In the overall plan of the church, the architect, Henry of Reyns, was mainly taking his ideas from earlier cathedrals built in northern France, especially the cathedrals of Chartres, Reims, and Amiens, which had just been built. Like the French cathedrals, Westminster Abbey has a round apse with radiating chapels, rose windows, and flying buttresses. Although this nave more or less follows the original plan from 1245, it was actually built a hundred years later, in 1376 - they had to stop for a hundred years to raise enough money!
The vault of the roof, indeed, shows that the nave was not built until the 1300s - it is a later Gothic style. The vaults are fancy ones with a lot of unnecessary ribs just to look more beautiful. From the outside of the church, we can see how the builders held up a heavy stone roof when the walls had such big windows in them - by using flying buttresses. To buttress means to hold something up, and you can see the flying buttresses - they are stone arches pushing against the walls to hold them up. At the bottom end of the flying buttresses they connect to regular non-flying buttresses which also hold up the roof.