A49 exit Thais, D531 east through Pont-en-Royans and Choranche to the Bournillon dam.
A48 exit Grenoble Nord, south to Sassenage, turn right on D531 west through Lans-en-Vercors and Villard-de-Lans to the Bournillon dam east of Choranche.
About half an hour walk to the cave entrance.
L=7,886 m, VR=65 m, A=418 m asl.
Portal: H=105 m, W=60 m.
|As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
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The Grotte de Bournillon is definitely a wild cave, but it is what is called a beginners cave. To enter the six kilometer long, almost horizontal cave with full caving gear is a fine and easy tour for the beginning or end of a trip to the Vercors. Or for a group of beginners under the guidance of some experienced cavers. But the entrance area is spectacular and so easy to visit, it can be recommended for the average tourist, who is able to walk on uneven ground.
To reach the cave there is a little walk necessary. Follow the road to hydroelectric station at the upper end of Bournillon lake. There is a gate so park the car in front of the gate where possible. The water for the power station comes through thick steel pipes from the east. There is no dam with a lake, the water is collected directly from a karst spring. This is an impressive karst related sight in its own. After crossing below the steel pipes follow the trail uphill towards the water fall Cascade de Moulin Marquis.
The entrance portal of the Grotte de Bournillon is located at the foot of a vertical limestone cliff. Left of the entrance is the Cascade de Moulin Marquis, where a small brook falls down the white cliff faces depositing yellow crusts of tufa. The entrance portal is said to be the biggest cave entrance in Europe. Its size is 30 m wide and 80 m high. The cave entrance is a seasonal karst spring which flows only during spring and after heavy rains. That's the reason why it is also known as Résurgence de Bournillon (Bournillon Spring). The trail is higher than the river flowing out, so it is possible to visit the entrance areas even if the spring flows. When its dry its also possible to walk through the riverbed.
Behind the entrance hall, a 2.5 km long tunnel of impressive dimensions follows. It ends at a siphon, which is open only during very dry periods of the year, for example in winter. The whole cave is often water filled, it is not advisable to visit the cave after snow melt or after heavy rains. Even the entrance area might become dangerous. However, there is a trail to the cave and into the cave which is pretty safe, and it is a matter of common sense to turn around when this trail is flooded.