A gently sloping ramp is generally the safest way to traverse a slope. A hand rail would add stability (and might be required by local building codes; check to make certain.) Large stones can be placed into a slope as steps, but usually this requires the assistance of a professional landscape contractor with special equipment to handle the large stones. A great deal depends on the steepness or grade of the slope. It may be money well spent to consult with a landscape contractor.