Mathematicians at Roskilde University and the University of Waterloo announced that, using the Open Source Routing Machine (OSRM), they have solved this staggering version of the traveling salesman problem (TSP)—a centuries-old mathematical challenge. They found an optimal path through all 81,998 bars across South Korea. And not just a good path, but the very best one: not a single second can be made to it.

“It is not possible to rearrange the order of stops to save even a single second of the OSRM-estimated walking time,” the researchers stated.

The total journey, they found, would take 15,386,177 seconds, or about 178 days, 1 hour, 56 minutes, and 17 seconds—provided you never stop for more than a sip of water.

How They Solved It

The Traveling Salesman Problem (TSP) is one of the most iconic and deceptively simple challenges in mathematics and computer science. At its core, the problem asks: what is the shortest possible route that visits a set of locations exactly once and returns to the starting point?

While easy to grasp, solving it efficiently becomes mind-bogglingly complex as the number of locations increases. It also has real life applications ranging from optimizing delivery routes, planning efficient manufacturing processes, scheduling satellite observations, mapping genome sequences, and designing microchips.

The main issue is that number of possible tours grows faster than you’d imagine. For this Korean pub crawl, the number of possible paths is about 2 followed by 367,308 zeroes—a number so large it makes the atoms in the universe look countable.

These problems are so large you can’t just brute force calculation. As the Washington Post once put it: “It would take a laptop computer 1,000 years to compute the most efficient route between 22 cities, for example.”

But brute-force guessing isn’t how modern mathematicians tackle the TSP.

The research team combined two sophisticated techniques: the LKH code for generating exceptionally good approximations, and the Concorde TSP Solver, which uses a strategy called the cutting-plane method.

Instead of locking in one road at a time, the cutting-plane method first allows fractional travel along multiple paths. Only gradually, with increasingly sharp constraints, does the algorithm home in on a final, indivisible route—the one true path.

Between December 2024 and March 2025, researchers used the OSRM to estimate walking times between every pair of bars, generating a colossal table of 3,361,795,003 travel times. They then applied their algorithms to sculpt these millions of possibilities into a single, perfect loop.

OK but… why?

At first glance, the project sounds like an academic stunt or a pub-crawler’s fever dream. But the traveling salesman problem isn’t just about maps and bar hops. It’s at the heart of how we optimize our increasingly complex world—from routing Amazon deliveries to scheduling telescope observations, even to designing computer chips. Each solution can help us finesse algorithms and pushes the frontier of what’s computationally possible.

“The world has limited resources and the aim of the applied mathematics fields of mathematical optimization and operations research is to create tools to help us to use these resources as efficiently as possible,” the researchers note.

It’s also a great way to get people more interested into math. It’s often said that mathematics is unattractive… well what’s more attractive than a pub crawl? In 2021, a similar tour through 57,912 locations in the Netherlands set the previous world record. This new Korean pub crawl surpasses it, marking the largest road-map TSP ever solved to provable optimality.

An interactive map of the full tour has been made available online. You can zoom into city clusters or pan across sprawling countryside, where the tour delicately stitches towns together like beads on a necklace.

In doing so, the work serves as both a technical landmark and a gentle reminder: even in a world that sometimes feels chaotic and messy, patterns of astonishing order can be found—or created—with enough ingenuity and perseverance.

And if you ever find yourself with six months to spare and a sturdy pair of shoes in South Korea, the route awaits.