The hapless driver stepped out of his Land Rover Freelander after parking at a beauty spot but forgot to put the handbrake on.
Seconds later, the vehicle rolled forward and coasted a whopping 250ft (76m) down a steep bank at Holne on Dartmoor in Devon.
The owner watched as the four-wheel drive bounced and bobbed its way through a collision course of rocks and scrub, coming to rest in a ditch.
His silver off-road jeep seemed to have escaped largely undamaged - until it began to sink in a muddy bog.
Eyewitness Nicholas Clegg, 52, an accountant from Yeovil, Somerset, saw the incident during a day trip with his son.
He said: 'The driver had left the handbrake off and the car had just rolled all the way down.
'I can't believe it managed to stay on all four wheels. At one point, the slope gets so steep that it's a miracle it didn't turn over.
'The only way would be to winch it all the way back up but it would require at least 200ft of cable and probably a helicopter.
'They would have had one heck of a job towing it out. It was a very wet valley and the car was well and truly stuck.
'The driver was devastated because it is a new car and although there was no superficial damage I dread to think what it's like underneath.
'It's every driver's nightmare. It's a good job it was an off-road vehicle otherwise it would have been completely written off.'
Rescuers were attempting to free the car.