Millions of years ago, the Paris Basin was covered by the sea. In order to see for himself, Enlarge your Paris journalist Rémi Belot set off on "the Crossing of the sands", a 12-mile route in Essonne between La Ferté-Alais and Étréchy stations.

With its golden dunes and fragrant pines standing proudly amidst oak trees, Paris Region sometimes has a hint of the Basque or Landes coasts, bringing back childhood memories of summer camps. Indeed, it's in the heart of Essonne, just a short distance from the small village of Boissy-le-Cutté, that you'll find this almost maritime landscape.
This is both surprising and totally logical: some 30 million years ago (and since the Paleozoic era, some 400 million years ago), the Paris Basin was a little more than a basin, since it was home to a sea... As the quartz decomposed, it left behind the fine sandy expanses that can also be found near Fontainebleau, among other places.
This astonishing geological curiosity has its own hike: the Crossing of the Sands. A 13-mile stroll through the fields from La Ferté-Alais station. After a few miles, the first climb emerges just outside the village of Huison-Longueville. We climb up to the Butte Hébert in the woods on a well-shaded path. A gentle 3% gradient over a distance of around 1.24 miles brings us to a plateau that lets us rest our thighs and calves. While our legs relax, our eyes take in the panorama: clearings and fields as far as the eye can see, with the melody of the wind in the vegetation as the soundtrack. Better than a session of relaxation!

Sand in sight!

As we enter the forest again, we come face to face with a pretty rocky chaos. Huge sandstone boulders mark the edge of a small cliff from which you can see the roofs and church of Boissy-le-Cutté.

What a view!

The descent to the village is steep via a small sandy track that slaloms through trees and ferns. And it's just past the village of Boissy, at the foot of the Butte blanche, that you discover the beautiful stretches of sand that give the trail its name.
It's time to leave your hiking boots behind - momentarily - and hit the dunes barefoot. An invigorating little treat!
The end of the trail may lack sand, but it doesn't lack salt. The route passes through the Butte du Puits geosite, a 20-foot-high former quarry. Just nearby: the Sarrazin hole, a small cave carved out of the rock. All that's left to do then is to take a beautiful stroll through the woods and cross the calm green waters of the Juine before reaching the Étréchy train station.
The sandman shouldn't be long in coming tonight...

Rémi Belot
© Rémi Belot pour Enlarge your Paris - Traversée des sables