Grotto, Underground Garden and Bridge about 60m to west of Dewstow House

The main drive is carried by a balustraded segmental arched bridge which crosses a winding stream which emerges from a stonework Gothic arch. This arch leads to a small 'gorge' with tiered rockwork on either side and the stream running in small winding channels in the level artificial rockwork floor, creating stepping stones through the arch. In the east side is a small semi-circular pool. An arched entrance leads to a winding rockwork passage into an underground garden.

Just inside the entrance of the garden, on the right hand side, is a caved-in passage into the underground garden to the east. Most of the floor is taken up with a naturalistic pool, with stone steps across it. There are pillars of rockwork with niches for ferns, and at the north end is a waterfall which is said still to work. The chamber is top lit but the glazing has gone, leaving only the iron and re-inforced concrete framework. The water for the gardens was carefully controlled and there are various standpipes and water cocks hidden in the niches. This garden was intended for growing ferns, a speciality of Henry Oakley's.