A full moon hoists itself beneath a dense black ledge of clouds overhead, revealing the best place to cross the swollen rivers. We can’t believe our luck. The downpour that has assailed us since dawn has stopped just in time for our trek along this deserted beach. Fringed by a jungle of palm trees on one side and the Pacific surf on the other, and intersected by numerous rivers Ostinal Beach on Costa Rica’s Nicoya Peninsula, this is one of the world’s most famed “arribadas” beaches. Here, four to 10 times a year between July and November, Olive Ridley turtles trundle ashore by the thousands to lay upward of 80 eggs each before returning to the sea.

Observing one of these mass egg-laying phenomena has long been at the top of our must-do list, but we’ve been following our guide Jorge for an hour and one thing is fast becoming clear: there will be no arribadas tonight. Now, we’re just hoping for even one turtle sighting, though we remain optimistic. Thirty-five to 40 kilograms in weight and 60 to 75 millimeters in length, an Olive Ridley may be one of the smallest of the world’s marine turtles, but it’s still plenty big enough to stub a toe on.

October is a risky month to travel Costa Rica’s roads. Infamous for being impassable at the best of times, they are also bereft of directional signs. In “Green Season,” the local euphemism for the May to mid-November monsoons, the country’s backroads turn into truck-sucking quagmires traversed mainly by marauding rivers. We left our Samara resort at daybreak, allowing five hours to drive just 50 kilometres. We also tried to locate a guide and a place to overnight at the beach, but the translated messages were vague. Something about the Nosara River being impassable by car . . . and “Si, Si,” someone might meet us on the other side to take us into Ostional and arrange a licensed guide.

Five hours later, the sheeting rain had slowed us into first gear and driven all possible sources of directions indoors. Were we even on the right road? When a raging river appeared suddenly in front of our windshield, we were ecstatic: the Nosara?! We backtracked to a farmer’s home and parked the car, then set off on foot with umbrellas, backpacks and uncertain spirits into the sopping jungle. The blood-curdling roars of howler monkeys followed us as we slipped through the mud a half-mile to the river’s footbridge, our rendezvous point.

A driver finally appeared, as confused as we were but willing to try. He drove us several miles until another river cut his route in half. We thanked our mysterious rescuer, crossed this unexpected second torrent, and squished onward until we were met by a second driver, ushered into the back of his open truck and brought to a hostel where we waited until 10 p.m. Our hoped for tour time.

Jorge is signalling with the flashlight. We rush forward to see tracks leading to the banks of a rivulet. There’s our Ridley digging in the mud! Programed to return to the same stretch of sand each year, she has fallen down this rain-eroded bank and is unable to climb out. Jorge hefts her to the opposite bank. She crawls a short distance and begins to dig again with her back flippers.

We hug each other. The howler monkeys are back, roaring in the trees, but they no longer sound ominous. The universe has tipped toward us, and we can’t believe we are here at last, one hypothermic couple with a pathetic smattering of Spanish and non-English-speaking guide, yet we understand. We understand we are blessed. For two hours, while the moon spills its light and the valiant Ridley pushes her eggs into the deep, funnel-like hole she has scooped in the sand, we stand entranced. Crying from exhaustion, the Ridley then begins to rock, gathering momentum for gigantic slams on the nest, and then covering it with sand to protect the eggs from scavengers.

An hour later, we are still watching as she retraces her tracks, tumbling yet again down the riverbank to be rescued once more by Jorge, until at last, she bathes her face in the waves of the Pacific. Her ordeal is over.

Walking back, we keep smiling at one another, catching hands. How will we get back tomorrow? Who knows. Where will we find anything to eat in this tiny village devoid of tourists? Who cares. Stepping off the secure path, we have been given an unexpected gift.