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Drive to the Grotte di San Giovanni (south entrance) and park behind the small country church at the top of the road. From there follow the path that goes up, entering the gate where the cows are kept. Do not worry about the cows, but make sure you close the gate behind you.
Follow the same path for 15 minutes, and you'll find yourself on a clearing of the wood next to a rock wall. On the right side of teh clearing there is a path winding up toward the crag. You can recognize the sector Free Sex as it as it has a large cave. Once you're there continue walking at the base of the crag to reach Sexy Shop