“I ’ve been coming here for years and that’s the first time I’ve ever seen an osprey in flight,” announces a sixty-something biker dressed head-to-toe in leather and peering through a monocular.

There’s a group of birdwatchers forming outside a wooden cabin, Northumberland Wildlife Trust’s osprey project space, next to Kielder Waterside café. Chaffinches peck at seeds as a vole pops its head up from a grass verge and house martins glide in the pale blue sky.

“Look, there’s an oystercatcher. Get a photo, Ron,” another man in a camouflage T-shirt whispers, pointing at a red-beaked bird that perches elegantly on the building next door.

It’s all happening just metres from where I spent the previous night in Tower Knowe Visitor Centre’s car park. Having borrowed a seaside-themed campervan through Quirky Campers, a peer-to-peer rental platform, I came to Kielder, England’s largest man-made forest, to try a new visitor experience.

Until 14 September, a Forestry England-led initiative called the Forest Campervan Road Trip allows visitors to stay overnight in seven forest locations across England, including Kielder Forest. At Kielder, prices start from £15 per night for non-members and £14 for members. The maximum stay for the off-grid experience is 48 hours and those taking part must not leave a trace (some spots have toilets, but don’t expect showers).

Kielder Forest is on the border of Scotland, in Northumberland – its highest peak, Deadwater Fell, offers views from Lake District mountains to the North Sea coast. The forest’s first trees were planted in 1926 to create a national timber reserve and replenish stocks used in the First World War. Local miners and dockworkers were brought in to do the manual labour and given places to stay with their families.

Back then, Kielder was a vast marshland surrounding the Duke of Northumberland’s summer house, Kielder Castle. Plans were made to refurbish the castle in time for Kielder’s 100-year anniversary. But there were a few unexpected issues, so it is likely to reopen next spring. However, this year there’s a host of activities planned for the weekend of 5 and 6 September to celebrate the centenary.

I spend my first night camping at a car park next to the castle, then I hike part of a trail. There are several walking routes from this point – the 1.5-mile Gruffalo walk is popular with young hikers, for example.

Despite living less than two hours’ drive away, it’s my first time at Kielder Forest and already I’m wondering why: it’s majestic. Its 50,000 hectares (around 125,000 acres) of dense forest surround Kielder Water, Northern Europe’s largest man-made lake (by capacity), within a site that covers 65,000 hectares.

Walking beside a babbling beck in a drizzle, pinecones crunching underfoot, I’m hit by the sweet scent of moist bracken. Hoping to spot a red squirrel – Kielder is home to a significant portion of England’s population – I squelch down to Kielder Viaduct, but loop back as the rain gets heavier.

There are other wonders to enjoy after dark. Kielder is part of the largest protected area of night sky in Europe (Northumberland International Dark Sky Park), with its observatory hosting events throughout the year. They range from Space Kids: Light Year Academy, a family-focused workshop, to Late Night Discovery (£49pp), during which I learn about galaxies and planets, see Saturn through a telescope and ask astronomers questions about space.

Waking up in the thick of the forest, with only one or two other campers for company is another treat. In some ways Kielder doesn’t look like England – some compare it to the wilderness of Sweden or Canada – but having grown up on camping trips around Lake Windermere, it reminds me of the Lakes – but without the crowds.

When I’m invited by the Calvert Centre – an accessible outdoor adventure centre specialising in providing outdoor experiences to those with disabilities – to try a canoeing session, there’s no one else on the water. “I love this part of the lake. It’s so peaceful,” my guide, Dani, says, pausing from paddling for a moment to take in the view. There’s barely a ripple in the water, and, but for a few fishermen perched on the banks, there’s not another soul in sight.

On my final morning, I wake up and pull back the campervan curtains to see an osprey, its 6ft wingspan fully extended, circling above Kielder Water looking for trout.

It’s like a scene from an Attenborough documentary, seen unfolding from the comfort of my bed.

Booking it

Temporary campervan sites at Kielder Forest are £16 per campervan, per night for non-members (book in advance, most sites open until 14 Sept). The Kielder Castle site is open year-round (£15 per night) and you can pay on arrival, subject to availability. forestryengland.uk/kielder-forest; visitkielder.com.

More information

Quirky Campers campervan rental from £110 per weekend night, three-nights minimum, quirkycampers.com/uk/campervans/.