Park in the last accessible car park.
(S/E) Take the Chemin de la Grotte des Fées, which starts just above the car park. There are no particular difficulties along the route.
(1) Continue on the left, leaving the ruins of the Gigot farm on your right, and keep left at the next fork to reach the cave.
(2) Grotte des Fées: take your phone or, better still, a torch with you to venture into the cave. There are no difficulties inside, but watch your head as you go in. Enjoy the view of Brison-Saint-Innocent and the north of Lac du Bourget.
Continue south along the path. Be careful, the return via the Singe trail with a view of the lake can sometimes be a little tricky for younger children and you may need to help them. One section seems dangerous to me, close to the climbing routes of Brison-Saint-Innocent (risk of falling): it is located about halfway along the route on the right.
Go down to the Chemin des Combes.
(3) Continue on the left until you reach the first houses. The car park is about 50 metres away on the left (S/E).
