Terrace, Wall, Grotto and Underground Garden about 5m to north west of Dewstow House

To the west of the house is a formal terrace with stone walls on its west, north and east sides. The north wall has blank arcading and a circular stone built alcove at its east end. The low west wall has a circular turret incorporating an alcove at its south end. In the south east corner of the terrace, adjoining the west gable of the house is the formal balustraded entrance to the underground gardens. Curved wing walls topped by ball finials lead to steps down to a flat topped entrance with a central Tuscan column. The only other part of the gardens visible from above ground is the glazed roof which is behind the wall described above.

The entrance opens onto a narrow passage lined with artificial rockwork which leads to a large chamber to the north of the terrace. Halfway along the passage is a branch passage which leads to a blocked entrance flanked by Tuscan columns which originally led to a further chamber (where there is now a swimming pool) and thence to the basement of the house. At the entrance to the chamber is a Gothic doorway with the original oak door. The chamber or underground garden is top-lit with an iron framework disguised as rockwork supporting glazing which is now much damaged. The garden has much artificial rockwork and is made to appear like a limestone cave with pillars, stalactites, pools at ground level with goldfish, pools stacked in tiers, higher level pools and many niches for growing ferns. There are some formal elements, such as balustrading, and the supporting walls on the north and south sides are coursed, undisguised concrete blocks. Originally there were fountains, and cascades from pool to pool. At the north west end of the chamber a passage leads to steps up to an arch into an open tunnel (originally roofed), at the end of which are two blocked passages, one to the chamber to the west and one to the demolished chamber to the east.