Sitstart right under The Whey of the Warrior, low traverse to the left up to the left angle and continue in Whey Out West (without mantling up on the 'mushroom' by convention).
From the bivouac of Bourron-Marlotte, follow La Route de la Grande Vallée for 200m eand take La Route des Barnolets on the right. The boulder is 250m further, on the right of the path.