Princes Street Gardens is a large public open space occupying much of the valley to the south of Edinburgh's Princes Street and to the north of Edinburgh Castle. It is effectively divided into three parts. To the east of The Mound and the Scottish National Gallery is East Princes Street Gardens, while to its west is, unsurprisingly, West Princes Street Gardens. The latter is further subdivided by the railway lines running from Waverley Station into the main area to their north and the open areas around the lower slopes of Edinburgh Castle Rock to their south.
It is fair to think of Princes Street Gardens as the punctuation mark that divides Edinburgh's Old Town from its New Town and this helps give the Gardens its role as an integral part of the underlying structure of the city. This is no afterthought city park added on for a bit of greenery: in a very real sense Princes Street Gardens is the beating heart of Edinburgh, offering opportunities for relaxation and recreation, and forming the frame for the iconic views of Edinburgh Castle from Princes Street.
The area now occupied by Princes Street Gardens has seen many changes over the years. Originally it was simply a natural valley excavated to the north of castle rock by glaciers moving from west to east whose path was diverted around the rock. The same glacial action formed the raised "tail" or "spine" on which the Royal Mile now stands, and also dug out a corresponding valley to the south of castle rock, later occupied by Grassmarket and Cowgate.
By the middle ages Edinburgh's old town had become one of the most densely populated places on earth, and occupied an area that extended some way down the Royal Mile, ending where it met the boundary of Canongate, which remained a separate burgh until as late as 1856. The city also spilled down the southern slopes of the high ground to form Grassmarket and Cowgate. To the north, however, the valley remained open land, which continued all the way through what is now the New Town to the edge of Leith.
Edinburgh was repeatedly invaded by the English from the end of the 1200s to the mid 1500s (and again in 1650) and security became an increasing concern. The tactic of simply abandoning the city each time an army approached, then returning to rebuild after it left, could only go so far, and improving the defences of the castle became central to the wider security of the city.
Edinburgh Castle was deemed to be weakest on its north side, and in 1460 the young King James III ordered its defences to be improved by the building of a dam along the line now followed by North Bridge, at the east end of Waverley Station. Natural springs led quickly to the forming of the Nor' Loch, a water barrier that was in places significantly deeper than the height of a man, and which formed an impassible marsh at its western end.
For three centuries the Nor' Loch served as a defence and an amenity to the citizens of Edinburgh: and, later, as a place for trying witches and as a large and very convenient cesspit. By the mid 1700s it was becoming increasingly seen as a (literal) obstruction to the city's ambitions for a major expansion to the north. By 1764 records show the loch had largely been drained, and the land was dry enough to carry the piers of the North Bridge, the first major link between the existing Old Town and the hoped for New Town. Two years later, in 1766, work began in earnest on the New Town, based on plans drawn up by architect James Craig.
Craig's original plans showed a canal passing along the valley to the north of the castle, largely as a decorative feature. However, the building of The Mound, an enormous causeway constructed from spoil from the New Town development to form a second link with the Old Town put a stop to this. Instead much of the area of the Nor' Loch was developed into private gardens for the enjoyment of residents of Princes Street, only later becoming a public park.
The railway carved through the gardens in 1846, completing the pattern you seen on the ground today, which gives a garden of 8.5 acres to the east of the mound, and one of 29 acres to its west. Over the years Princes Street Gardens has become the focal point for both celebrations and commemorations. It is never busier than during the Edinburgh Festival each August, though the six weeks of the Edinburgh Christmas run it close. During this period East Princes Gardens becomes home to an ice rink, big wheel, funfair, German Market and a range of other attractions.
The gardens are also home to a fine collection of memorials and statues including, most obviously, the Scott Monument commemorating Sir Walter Scott. Look only a little harder and you can find the Scots American War Memorial; the Scots Greys Memorial; the Spanish Civil War Memorial; the Black Watch Memorial; the Royal Scots Memorial; and statues of or memorials to a number of individuals including Allan Ramsay and Robert Louis Stevenson. Plus a statue of Bum the Dog, San Diego's answer to Greyfriars Bobby.
It is easy to think that because something exists, it will always do so. The arrival of the railway showed that no open space within a city can ever be taken for granted. And Princes Street Gardens came very close to being changed out of recognition much more recently. In the 1960s proposals were seriously considered to build motorways through Edinburgh, in much the same way as was done in Glasgow. As part of a much grander plan, Princes Street would have been rebuilt as a two level street, with a third level, offering huge underground car parks, eating significantly into Princes Street Gardens. We can all be thankful this never happened.