Last week, two daredevil Canadian climbers, Will Gadd and Sarah Hueniken, attempted the impossible: scaling Niagara’s 51m-high, frozen falls. And it only took them just under an hour to do it.

Niagara Falls, the collective term for the three waterfalls that dominate the border between New York state and Ontario, Canada, flows at a rate of up to two million litres per second. Because of that immense volume, the falls almost never stop moving. In fact, other than a 30-hour dry spell on 29 March 1848, when an ice jam in the upper river blocked the regular flow of water, it was nearly unheard of until early 2014, when the falls came to a near standstill twice during the extreme North American cold wave. (And while some would argue that the falls froze in the early 1900s, the credibility of that commonly shared photograph has been proven questionable.)

It’s important to note that even in these three rare instances, the falls never completely froze over, making attempts to climb up the falls extremely dangerous. The water, albeit in smaller volumes, continues to flow, forming unstable layers of snow, slush and ice (see 2:08 when Gadd sinks his hooks into a piece of snow that simply crumbles away). It’s a feat we wouldn’t suggest trying at home. Still, for Gadd and Hueniken, being the first climbers to travel up Niagara Falls is a good way to go down in history. “There's only one Mount Everest, there's only one Niagara Falls and I feel really lucky because that ended a lot of hard work by a lot of people and I got to climb something to me that was really amazing and really beautiful and a whole lot of fun,” Gadd said in an interview with ABC.

In the winter, videos like the above are one of the only ways to get a sense of the falls’ majesty up close. Visitors have been banned from walking on the bridges formed by the ice since 1912; it’s illegal to climb the falls on either side of the border; and the boat tour on the New York side of the Falls, the Maid of the Mist, shuts down after October because of icy conditions, usually reopening in April or May.