No special access issues
The area is located between the towns of Isili and Nurallao, on the south end of the lake. Driving from Isili you'll spot the crags on your right-hand side. Take a sharp right turn before the bridge, and go down to the level of the water, following the dirt road until it goes over a little bridge. Park on the side of the road allowing space for other cars.
Pietra filosofale
At this point enter the gate (and close it after you) and follow the path at the base of all the crags. After 10 minutes you'll pass through a very narrow gate (1 meter wide), walk up to the left, to the base of this large crag.
Cubo Magico
Keep on walking and pass all the crags, after 10 minutes the vegetation opens up and you'll see the massive overhanging Corvo Solitario. Go that direction, pass the stream and then walk back following the stream, where you'll find Cubo Magico.