Grotte en Y

Grotte en Y is a small karst cave in the commune of Gondenans-les-Moulins, in the Doubs department, in the Bourgogne-Franche-Comté region of eastern France. It forms part of the Réserve naturelle régionale des grottes du Cirque, a regional nature reserve created to protect colonies of hibernating bats. The cave sits within a range of hills carved from Middle Jurassic limestone and is not open for visits.

Where exactly is Grotte en Y?

The cave lies within the commune of Gondenans-les-Moulins, in the Baume-les-Dames canton, in the north-eastern part of the Doubs department. The reserve's coordinates are roughly 47°27'46" N, 6°23'01" E. The landscape is classic karst country: hills cut through by dry valleys and small gorges known locally as "reculées," with layers of upper Bajocian limestone exposed at the surface.

What is the Grottes du Cirque reserve?

Grotte en Y is one of six cavities protected within the reserve, alongside Grotte aux Ours, Grotte du Four, Trou du Seris, Grotte sous le trou du Seris, and the resurgence point of the underground Seris river. Altogether the reserve covers about 15.3 hectares. The site was first protected in 1988 as a voluntary nature reserve, then upgraded to full regional nature reserve status by a decree of 24 September 2015, with a management plan approved in September 2019. Day-to-day oversight rests with CPEPESC Franche-Comté, an association dedicated to bat conservation and the protection of nocturnal habitats.

Where does the name come from?

The name "Grotte en Y" describes the shape of the cave's passages, which branch into two arms meeting at a single junction — a Y in plan view. Descriptive names of this kind are common among the karst caves of the Doubs, most of which were first mapped and catalogued by local caving clubs.

Can visitors go inside Grotte en Y?

No. The cave is closed to the public year-round, a rule that applies to all six cavities in the reserve with one exception. Only the resurgence of the underground Seris river can be entered seasonally, between 30 April and 31 October, and only with prior authorization from the Gondenans-les-Moulins municipality — an arrangement aimed at caving groups rather than casual visitors. Grotte en Y itself is not part of any visitor circuit and has no public entrance.

Why is the cave protected?

The whole complex is protected chiefly because of its bat populations. Nine species from the Vespertilionidae family have been recorded in the reserve, along with the lesser horseshoe bat and greater horseshoe bat, both listed as threatened on the regional red list. The dark, humid, thermally stable conditions inside caves such as Grotte en Y make them ideal winter hibernation sites, which is why any tourist access or disturbance of the underground microclimate is ruled out.

FAQ

Can I visit Grotte en Y on my own? No — the cave is closed to the public all year to protect hibernating bat colonies.

How large is the reserve that contains the cave? The Grottes du Cirque reserve covers around 15.3 hectares in the commune of Gondenans-les-Moulins.

How many caves make up the reserve? Six: Grotte en Y, Grotte aux Ours, Grotte du Four, Trou du Seris, Grotte sous le trou du Seris, and the Seris river resurgence.

Is there anything cave-related nearby that can actually be visited? Yes — the underground Seris river resurgence is accessible seasonally, from 30 April to 31 October, with prior authorization from the municipality.

Since when has the area been formally protected? Since 1988 as a voluntary reserve, and since 24 September 2015 as an official regional nature reserve.