Organisers don't want it to turn into a race and, besides, there's absolutely no running, we're told. It would wreck the millions of dollars worth of wooden boardwalk. This doesn't stop the youngsters from taking off like Usain Bolt when the starter's shotgun is fired.
The hike begins through forest at the entrance to Fiordland National Park. It descends to Bluecliffs Beach, and a wander for several kilometres along the sand at low tide. The head torches of a hundred hikers light it like a cityscape, and thousands of glow sticks dropped along the track ensure stragglers are not lost in the pitch black overcast night.
Soon we head inland and pass the first of many checkpoints. The lubricated volunteers, all dressed in assorted costumes, hand out chocolate pick-me-ups.
After a couple of swing bridges, comes the big climb. The steepening track spreads the field. Even in the dark the intriguing beauty of Fiordland is apparent, giant ferns and soaring nothofagus trees create a spectacular canopy.
By now it's around 3am, and the first wave of fatigue hits. The body wants to shut down, the mind is not far behind.
I reach another checkpoint where the marshall, wears a horror film costume. The track then hits its steepest stretch, and after a bit of a grunt we're on top of the ridge. A faint glow of lights at Okaka Lodge is now visible, and soon I'm resting in front of a fire savouring every spoonful of hot porridge.
Back out on the boardwalk there are no more glow sticks, and it's still very dark. I hope my headtorch battery lasts. This was my favourite stretch - no other hikers around and just the slightest hint of the Fiordland vistas to come.
It's impossible to get lost, and after a gradual descent on the tussocky steppe, passing through one of the seven distinct floral zones of the Hump Ridge Track, we re-enter the forest.
The sun is rising by the time I reach the 6.5km straight to Port Craig, an uninhabited collection of buildings that used to be New Zealand's busiest milling town. The rail track that used to transport timber there passes over three wooden viaducts which loom like bridges to nowhere. The largest, the Percy Burn Viaduct, is the world's highest remaining wooden viaduct, built in the 1920s.
Fatigue has returned, and every jolt of the knees on uneven rail sleepers intensifies the ill feeling. Now 9am, and more than 24 hours without sleep, the mind wanders to dark places.
Fortunately, the consistently cheerful checkpoint volunteers are great at alleviating the monotony.
The lunch stop at Port Craig brings a spirit-lifting supply of hot soup, sandwiches and coffee. More trampers come through and remove their shoes to mask the pain. The soles of one woman's feet are completely blistered. Suddenly I don't feel so bad.
No lingering now. It's the home run. The track winds down to the beach, and the feeling of relief at seeing the ocean again is immense.
A short walk along the shore, back into the bush then another hour of grunt and we return to familiar territory, rejoining the loop of the previous evening.
The final 30 minutes is agony, and I come home in just under 14 hours, an hour behind the fastest pair, which included the youngest entrant, a 14-year-old from just up the road.
River to the sea
Western Southland is emerging as a compelling adventure tourism alternative to Queenstown and a jet boat ride down the the Wairaurahiri River is a perfect way to venture deep into the wilds of Fiordland.
The 92km, six-hour trip leaves Lake Hauroko, New Zealand's deepest lake, at 10am.
History buffs will be in for a surprise. Sitting in a cave on an island in the middle of the lake is New Zealand's archaeological answer to the Egyptian mummies.
In the 1960s, the well-preserved skeleton of a Maori princess was discovered sitting upright, pointed north. She would have died around 1620, lived to the age of around 50 and enjoyed a healthy diet.
Under an agreement with local Maori, the remains have stayed where they are, but have, unfortunately, deteriorated in recent years. And although jet boating tours are not permitted to go near the cave, guide Johan Groter's informative commentary brings the legend to life.
The river falls 185m in its drop to the ocean, as it winds its way through grade-three white water rapids on the Wairaurahiri River down to the rugged south coast. As well as being an expert driver, Groter checks stoat traps and allows short bush walks into the uninhabited forest.
A delicious barbecue lunch at Waitutu Lodge is included in the price of $225 an adult. Johan can also pick up trampers or link to helicopter rides in and out of the region.
FURTHER INFORMATION
Midnight trampers: Next year's Stump the Hump will be on Friday, February 1, starting at midnight. Cost: $130. Bookings open around August at humpridgetrack.co.nz.
Wairaurahiri River jet boat trips: See wjet.co.nz.
Where to stay: Kirmington Dene, 90 minutes from Te Anau, is a luxury bed-and-breakfast set on a working farm. Contact Julie Sanderson on (03) 226 6630.
