MANGAPURUA TRACK — To avoid panicking, I focused on maintaining my balance and freeing my legs, which had disappeared up to my knees in mud. I gripped the handlebars and tugged fiercely as my bike’s rear wheel slipped toward an abrupt edge beyond which was a 200-foot drop to the meandering Mangapurua Stream. A limestone cliff, called Battleship Bluff, loomed overhead. One by one my fellow bikers and I attempted to walk our bikes across a fresh 20-foot-long mudslide, politely called a “slip” in this part of the world.

We were biking along the Mountains to Sea Trail on New Zealand’s North Island, in an area so dense, hilly, and remote that the native Maori never bothered settling here. Giant tree ferns, moss-covered beech trees, supplejack vines, and towering rimu trees created walls of vegetation so thick we couldn’t see a big valley or river until we were upon it.

The 200-mile trail starts on the slopes of a volcano, passes through two national parks (Tongariro and Whanganui), includes a jet-boat ride down a placid river, and ends at the Tasman Sea on the southwest coast. The trail has been designated one of the country’s Great Rides, similar to its famous multiday Great Walks like the Milford Track or the nearby Tongariro Circuit, which takes hikers past alpine lakes, up volcanoes, and along the lip of a steaming crater (including Mount Ngauruhoe, which starred as Mount Doom in “The Lord of the Rings”).

The Mountains to Sea route also forms part of Nga Haerenga, the New Zealand Cycle Trail, a new bike-path network that will eventually include 18 so-called Great Rides, mostly off-road trails stretching from Cape Reinga on the North Island’s northernmost point to Bluff, the South Island’s southernmost town. Once the cycle trail is completed, by the end of this year, bikers can explore more than 1,500 miles of paths that cut through some of the country’s most stunning landscapes.

With our time limited, four of us signed up to do a 22-mile section that included the Mangapurua Track and the Bridge to Nowhere extension. The Mangapurua Track had only recently opened to mountain bikers when we tackled it in November, having until then served mainly as an access trail for hunters. Even our guide had only cycled it once before, and he approached it from the opposite direction.

Our group of New Zealanders and overseas visitors included mostly intermediate riders. I recommend having a significant amount of confidence on a mountain bike before attempting this challenging route. One woman in our group, a Kiwi, was a first-time mountain biker, but she was strong and athletic and ran a sheep and cattle station with her husband, so she understood the wild landscape and how to navigate it.

Our plan was to drive an hour south of National Park Village, the main “town” for the Tongariro and Whanganui parks, to a remote access point 19 miles down Ruatiti Road. This one-lane, twisting gravel road had treacherous drops and no guardrails, and was not designed for those with vertigo or motion issues. We would then bike 22 miles through the wilderness to a boat landing on the Whanganui River. Here, we would meet Richard, a local farmer who would whisk us by jet boat more than an hour up river to Blue Duck Station, a remote farm and conservation area where we would find hot showers, a home-cooked dinner, and cozy beds in our own private lodge. The trick: We had to meet Richard by 4 o’clock in order to make it back by dark; in these parts, you can’t see a thing on the river at night.

The ride started with a one-hour uphill grind until we reached a sign marking the entrance to Whanganui, the country’s newest national park, established in 1986. It was all downhill from there, as the trail cut through virgin rain forest and abandoned farmland that had been settled by returning servicemen after World War I. The government leased pieces of land to these men, nearly 40 in all, who set off with their backpacks and high hopes to make a go of it in the bush, building homes and farming the wild terrain. Most walked away within the first few years. By 1943, all had left.