At 876 feet high and more than 3,000 feet long, the New River Gorge Bridge is an engineering marvel. (Becky Krystal/TWP)

There are heights. And then there are heights.

In the former category: Metro escalators, ski lifts, my attic.

West Virginia’s New River Gorge Bridge, on the other hand, is decidedly in the latter. The engineering marvel in southern West Virginia, completed in 1977, checks in at 876 feet high, and I was going to walk across it.

Or, I should say, beneath it. A catwalk running below the roadway recently opened for guided one-way tours, an activity conceived by self-proclaimed “bridge troll” Benjy Simpson and his team at Bridge Walk.

The prospect of a two-foot-wide strip of metal separating me from a fatal plunge into the river terrified me only slightly. But for someone who can suffer a bout of vertigo just looking through Washington’s sidewalk grates, it was a bit of a risk.

To steel myself for the challenge, I visited Hawks Nest State Park, about 4.5 miles northwest of the bridge, where an aerial tramway ferries visitors from the park lodge to a marina along the lake below.

I climbed into one of the cars for the nearly 500-foot ride. A few seconds after the steep descent began, the speed picked up more than I thought it should. My breath caught in my throat, and I braced myself against the wooden seat. This was an inauspicious start.

I arrived at the bottom safely, if a little wobbly-legged. After admiring the pretty greenery beside the lake, I contemplated hiking to a waterfall, until I learned that it was nearly a mile away. The thought of conveniently missing the last tram was tempting, but I decided that the trek up to the lodge by foot would be even more taxing than the return ride.

Leaving the park, I decided to prepare a bit more by driving over the New River Gorge Bridge on my way to my digs in Fayetteville. Crossing the bridge, though, takes less than a minute and doesn’t offer much opportunity for gawking at the gorge, which has an average depth of 1,000 feet as the New River flows north from its North Carolina origins. So much for all my prep work.

In the morning, I visited the Canyon Rim Visitor Center, one of two centers at the New River Gorge National River, a 70,000-acre park run by the National Park Service. A scenic overlook provided a panoramic view of the river and the bridge. Wispy little clouds hung within the gorge. Finally, I could appreciate the scale of the structure and why it took three years and $37 million to complete the 3,030-foot span.

Later, I joined seven other daredevils at the Bridge Walk office, where we signed liability-release forms and put on our harnesses, complete with a separate strap for our cameras. Smart, very smart.

A bus took us to the tour’s starting point. Our guide, 17-year-old (!) Sidney Crist, gave us some history and statistics before we started. I tried to take it in, but I was finding it hard to do anything other than stare at the bridge.

Walking on the span as a tourist works like this: A carabiner (metal loop) connects the harness around your waist to a lanyard. At the end of the lanyard — more like a leash — is another carabiner attached to a transfastener, a gadget that rolls along one of two parallel steel wires above the catwalk. And, of course, there are railings on either side of you.

I shuffled along the first part of the walk with my hands on both rails, giddily laughing a kind of oxygen-deprived nervous giggle that reminded me to breathe regularly. I wasn’t the only one holding on. Angela Murray of Cleveland, a good sport who was taking the tour with her father and siblings, clasped the rails every time the bridge began to shake from the traffic overhead. I couldn’t blame her; it felt like earthquakes I’ve experienced.

Simpson told me later that only three of the more than 1,000 people who have embarked on the tour couldn’t finish it. I doubt that any of us wanted to be the fourth.

We slowly made our way along the catwalk, stopping periodically to take photos and listen to Crist explain the bridge’s mechanics: how it can absorb the weight of the traffic overhead, how it expands and contracts based on the season, and how inspectors climb through some of the beams looking for damage. He did this while skillfully maneuvering over the handrails to stand on the bridge’s W-shaped beams so that we could all hear him.

The real payoff came once we found ourselves standing over the river, which snaked below us between the steep green banks of the gorge. I saw a kayaker and two rafts navigate the rapids, the vessels so tiny that it felt as if I was watching a model-railroad version of reality.

After a little more than an hour, we reached the end. Crist clambered up a rock to snap individual photos of us with the bridge in the background. That look on my face?

Pure relief.