I park at a precarious 45-degree angle in the chalky car park above Lulworth Cove, a perfectly circular bay carved into the cliffs. Locating the kayaks proves less of a challenge – they’re stacked in neon yellow glory to the side of the car park, where two tanned surfer types are surrounded by a gaggle of sunburnt tourists. Terry, who runs the tours, and Paul, who will be our guide for the afternoon, break off battling with the unwieldy kayaks to help us get kitted up. As we heave on fetching grey salopettes, Terry keeps up a running commentary on where we’ll be paddling (west past Durdle Door to Bat’s Head), what we’re likely to see (dolphins were spotted on an evening tour the previous week, and gigantic spider crabs can often be seen in the seaweed at Man o’War Bay) and the geological history of the area. The Lulworth Crumple, a huge fold in the rock, can be seen at several points along the coast, and if we were to paddle east out of the cove we’d arrive at the Fossil Forest, where ancient tree stumps and dinosaur footprints are preserved in the cliffs.

Paul gives us a brief introduction to the art of paddling (how to go forward, not sideways, and where to find Park and Reverse) and the next thing I know we’re afloat on the chilly, weedy waters of the cove. Sure enough, I notice an elaborate knot of twisted bedding planes, just as Terry described. Fortunately the kayaks prove easy to manoeuvre, responding obediently to the dip of my paddle, and we quickly shoot out of the bay and round the headland to the neighbouring inlet, Stair Hole.

This is a Lulworth in the making – a baby cove, with a dramatic double-arch entrance. I’m both unnerved and exhilarated as I paddle beneath I-don’t-know-how-many tonnes of limestone into the tiny boulder-strewn bay. There’s just enough room for the group, with an ethereally lit cavern to one side and another arched rock formation to the other. Paul allows us time to explore the nooks and crannies before rounding us up for the paddle past St Oswald’s Bay and Man o’War Bay (home to the giant spider crabs; I’m relieved not to spot any) to Durdle Door itself.

It towers above us, arcing imposingly across the sky. As I paddle beneath I’m stunned by how slender the limestone span appears, and reflect that this would not be a good moment for it to cave in. Fortunately it doesn’t, and we paddle on towards the solid chalk headland that’s our final destination. Bat’s Eye, the tiny *** in the foot of Bat’s Head, is our final challenge, and navigating the narrow passage proves our trickiest manoeuvre of the day. But the pebbly beach on the far side can only be reached from the sea, so we find ourselves alone for a brief (and cold) dip and a swift, energizing Mars bar.

It’s a 45-minute paddle against the tide back to Lulworth, and I’m exhausted when I finally ram the nose of my kayak up the shingle beach and stagger to the shore. I know my shoulders will feel like an arthritic 80-year-old’s in the morning, but I’d do the trip again in a heartbeat.