Bristol Bridges Walk

The Bristol Bridges Walk is a circular hiking route that is linked to the Königsberg bridge problem, a mathematical puzzle, which laid the foundation for graph theory, the mathematical study of networks. The Bristol Bridges Walk presents a solution of the puzzle for the city of Bristol. Its route leads the walker through different quarters of the city, the Avon Gorge and Leigh Woods. Along the way it crosses 45 bridges including Clifton Suspension Bridge, Bristol Bridge, and Avonmouth Bridge. The walk featured in various charity fundraisers of which the Bristol Giving Day 2019 is perhaps the most notable.

Historical puzzle
The Königsberg bridge problem is a mathematical challenge from the 18th century. It asks to find a route that leads the walker across each of the seven historical bridges in the city of Königsberg such that each bridge is crossed exactly once. The seven bridges in the historical puzzle connect the two banks of the river Pregel and two river islands, but their particular configuration makes it impossible to cross all bridges without crossing at least one of them more than once, making the puzzle unsolvable. It has been suggested that the bridge problem was never a serious problem but rather a prank that the intellectual elite of the 18th century Europe played on each other.

In 1735 the challenge reached Leonhard Euler at the Academy of Sciences in St. Petersburg. Euler realised that it is easy to show that no solution exists using a brute force approach. However he wanted to find a more elegant proof, which led to a new approach that Euler called Geometry of Position. Euler's solution was so elegant that it inspired many subsequent works. These works eventually evolved into several major branches of mathematics including topology and graph theory.

Original bridge walk, reception, and variants
In 2013 network scientist Thilo Gross realised that the city of Bristol has a similar configuration as Königsberg, with the city occupying two river banks and two river islands. In Bristol one of these is Spike Island, whereas the other consists of Redcliffe and St Philip's, which were historically separate, but are now joined by a land-bridge. Gross then began to explore if the bridge problem is solvable in Bristol. This posed an interesting modelling challenge as criteria needed to be developed, what structures qualify as bridges in the sense of the challenge. After a first failed walk attempt during which he discovered an additional bridge, he eventually arrived at a list of 42 bridges within the city boundaries that would likely have been included in the original Königsberg problem.

On February 23, 2013, Gross completed the challenge by going on a walk that crossed each of the 42 bridges exactly once. The original route of the walk started on Spike Island and ended with the crossing of Clifton Suspension Bridge into Clifton as a circular walk wasn't possible at this time. Since the original walk, three new bridges have been constructed (Brock's Bridge, St Philip's Footbride, Bathhurst Basin Bridge West), leading to the present number of 45 bridges. As a result a circular walk has become possible and the length of the walk has shortened slightly to approximately 30 mi. An alternative route that is suitable for mobility scooters has also been published by Jeff Lucas.

The walk received coverage in local newspapers, magazines  and was further popularized in a book and also featured in a number of charity fundraisers and events, including Let's Walk Bristol, Bristol Walk Fest and Bristol Giving Day as well as smaller events.

Route
The walk starts in Bristol's Castle Park by crossing Bristol Bridge, the oldest of the bridges. It briefly returns to Castle Park one more time by crossing St. Philips Bridge and Castle Ditch Bridge and then moves back and forth across between the quarters of Redcliffe and Old Market via Temple Bridge and two modern bridges named Valentine and Meads Reach Bridge. The architecture along this stretch is dominated by storehouses from Bristol's merchant past, but becomes increasingly modern closer to Bristol's commercial district. A highlight is Brunel's Temple Meads railway station through which the route passes.

The next bridge on the route is Bath Bridge, a double bridge consisting of two separate structures that are both crossed. The route then continues along a modern hiking and cycling route underneath the platforms of Temple Meads station and via two of the newest bridges, Brock's Bridge and St. Philips Footbridge. It then continues on a footpath along a stretch of Bristol's New Cut to the blue Temple Meads Relief Line Bridge. The route passes the TV studios in the old paintworks area before crossing the New Cut again via a rope suspension bridge. The route then continues through Sparke Evans Park to St. Philip's Causeway Bridge. The route crosses through St.Philip's Marsh to the Feeder Canal, where the it uses Barton Hill Bridge to cross into Netham Park. At Netham Lock it rejoins the River Avon and crosses New Brislington Bridge into the suburb of St. Anne's. The path continues along disused docks that are remnants from the Industrial Revolution to St. Anne's Footbridge, the easternmost point of the walk.

From St. Anne's the route makes its way back to the city center via Feeder Road Bridge, Marsh Bridge and Totterdown Bridge. After a brief visit to Victoria Park it uses Langton Street Bridge, better known as Banana Bridge due to its shape and bright yellow color. The path crosses the New Cut two more times on Bedminster Bridge, another double bridge, before crossing over to Spike Island on a bridge known as 'the blue caboose' or Ostrich Bridge, after the nearby Ostrich pub which contains an entrance into the Redcliffe Caves. The route now reaches Bristol's Harbourside area, where it crosses the two sides of Bathhurst Basin Bridge close to the historic Bristol General Hospital building. The route uses the Gaol Ferry Bridge and then the steam-age industrial Vauxhall Bridge and finally Ashton Avenue Bridge. The path then leads across the New Cut and the Floating Harbor via a complex circuit that involves two major bridges, Avon Bridge and Plimsoll Bridge as well as several minor bridges beneath them. One of these minor bridges is known as Brunel's other bridge as it was designed by Isambard Kingdom Brunel.

The route continues up the Hill to Cliffton Village. Here it crosses the Clifton Suspension Bridge, which soars 331 ft above the waters of the Avon. On the other side the path descends through Leigh Woods into the Avon Gorge. The route follows an old towpath to the village of Pill where the largest and westernmost bridge of the walk is located. Avonmouth Bridge carries the M5 motorway 538 ft across the Avon. It has a foot and bike path separate from the road.

The path returns to central Bristol via a path that leads along the beaches and woods on the bank of the Avon and past the Horseshoe Bend in the River Avon. It continues to the town of Sea Mills where it crosses the Portway Trym Bridge. From there it continues to the open fields of Durdham Down. The route uses Cumberland Basin Bridge to return to Spike Island where it passes Brunel's SS Great Britain and Banksy's Girl with the pierced eardrum before leaving via Prince Street Bridge. The route then goes past the harborside entertainment venues over Pero's Bridge and on to Victoria Square. It crosses over to Redcliffe a final time using Redcliffe Bridge before crossing at the modern Castle Bridge returning to the starting point in Castle Park.