(CNN) — A whitewater wonder visited by everyone from Marilyn Monroe to Mark Twain, Niagara Falls has been a magnet drawing global travelers for at least two centuries. But until this year, a huge tunnel buried deep below the cascade has been off-limits to visitors.
The rocks beneath the gigantic triple waterfall that straddles the border between the US state of New York and Canada's province of Ontario are honeycombed with chambers carved out to harness the powerful forces of nature thundering overhead.
And now, a 670-meter (2,198-foot) tunnel built more than a century ago on the Canadian side has been opened up to reveal the awesome scale of these engineering marvels.
Since July 2022, it's been part of tours of the decommissioned Niagara Parks Power Station tour which began a year earlier. Exploring it offers a fascinating glimpse into pioneering work that helped bring this corner of North America into the modern age.
The power station, which operated from 1905 until 2006, diverted water from the mighty Niagara River to run giant generators that electrified regional industry and contributed to the nearby Great Lakes port of Buffalo becoming known as the City of Light.
The region around the waterfall, according to station tour guide Elena Zoric, was once a hub of activity for businessmen who wanted to cash in on harnessing hydro power.
The Adams hydroelectric power plant was the first to open, operating on the US side from 1895 to 1961. On the Canadian side, the Ontario Power Company operated from 1905 to 1999, and the Toronto Power Generating Station from 1906 to 1974.
The 670-meter tunnel was carved out of the rock more than a century ago.
Today, the Niagara Parks station is the world's only fully intact hydroelectric plant of its era. Originally operated by the Canadian Niagara Power Company, it used Westinghouse generators to create alternating currents patented by inventor Nikola Tesla -- cutting-edge technology at that time.
The plant, as tour guide Zoric explains to visitors, was built at a time when aesthetics ruled. Its rustic limestone exterior and blue roof tiles were, she says, an attempt by New York architect Algernon S. Bell to make the structure blend in with the falls.
Before reaching the tunnel, visitors to the power station are shown a scale model of the massive engineering works that went into converting the pounding waters into electricity.
Cyclindrical blue generators once converted the force of the water into electricity.
Zoric shows where the water came in, where it ran down a shaft to power the turbines, and then where it went through a tunnel to a discharge point at the base of Horseshoe Falls, the largest of Niagara's three cascades.
Marcelo Gruosso, senior director of engineering and operations with the Niagara Parks Commission, has been involved with the project since it was first envisioned in 2017.
"The plant started out with two generators and, by 1924, all 11 were installed, which you see here today," he says, walking through the high-ceilinged building to point out a line of blue, cylindrical generators that fill the space.
"Beside every generator is a 'governor' which regulated the waterflow to a turbine. An air brake in the governor helped adjust the flow. They needed 250 rpm exactly to give them 25 hertz."
One of a kind
The tunnel once held 71,000 gallons of water moving at nine meters per second.
A glass elevator takes visitors down 55 meters past the six levels of infrastructure required for the hydro power generation process. At the bottom is the tunnel where the water would exit.
The tunnel, which is almost eight meters tall and six meters wide, is also an historic, one-of-a-kind attraction and is included in the power plant's price of admission.
"It took thousands of workers four years to excavate the shale beneath the main generating room using lanterns, dynamite, pickaxes and shovels," says Gruosso.
"On its way down, the water would spin the turbine blades," says Gruosso. "They were connected to a 41-meter-long shaft that went all the way back up to the main floor and spun the rotor in the alternator, generating the AC power."
Walking along the tunnel's arched passageway, he gestures to chalky white marks that reach almost to the top of the arched brick walls.
"You can see how high the water went," he says. "The tunnel held 71,000 gallons of water that moved at nine meters per second."
Built like a fortress, the gently curving tunnel comprises four layers of brick and 18 inches of concrete and is surrounded by shale.
"It's amazing what they did with no electricity," notes Gruosso.
"We did some minor brick repairs and added rock anchors to the arch to ensure structural integrity, but it's in really good shape. They only ever did maintenance twice since it was built, once in the 1950s and once in the 1990s."
Tourists can now walk out onto a platform to view Niagara Falls.
Near the end of the tunnel a rumbling begins to fill the air. Natural light pours in as the path exits onto a 20-meter, river-level viewing platform that is almost at the base of Horseshoe Falls. Gruosso has to shout to be heard over the ceaseless pounding.
"This is where the water from the tunnel poured into the river. It's the best place to see the falls."
The platform also gives visitors a perch to watch the tourist boats, filled with passengers in rain-ponchos, bobbing like corks at the foot of the falls.
To round out the power plant experience there's an evening show titled "Currents: Niagara's Power Transformed." The light and sound experience outlines the power plant's history and includes 3D projections of surging water, turbines and sparks of electricity.
A visit to the power station and tunnel takes around two hours, but to attend the evening show an overnight stay is recommended. Accommodation ranges from higher end Falls-view hotels such as the Hilton, to budget-conscious establishments like the Days Inn.
As for dining, Niagara Falls was once strictly a hotdog and fries kind of town. Fast food is still around but the destination has upped its game. Chef-inspired, locally sourced menus are available at Niagara Parks establishments including Table Rock House Restaurant as well as independent dining spots such as AG which features produce from its own farm.
Also worth checking out is the Niagara Parkway, which winds along the Niagara River and can be explored on foot or by rented e-bike. Stops along the way include Whirlpool lookout point and the Sir Adam Beck Generating Station, a monolithic structure along the river that currently contributes to southern Ontario's electrical grid.
A trip to Niagara Falls is energizing in so many ways. It's a place of natural beauty but it can also make you think twice about the natural forces that continue to shape our modern lives.