The Lower Terrace is cut by a wide ramp leading to a large courtyard at Middle Terrace level and a smaller ramp leading to the Upper Terrace (unfortunately closed to visitors).
Visitors are allowed to visit the upper terrace on special occasions only.  
mnli hypothesis: Visitors are allowed to visit the upper terrace on special occasions only.   premise: The Lower Terrace is cut by a wide ramp leading to a large courtyard at Middle Terrace level and a smaller ramp leading to the Upper Terrace (unfortunately closed to visitors).