Dewstow House (nprn 36809) is located to the immediate north-west of Caldicot, on the north side of the M48 motorway. It is noted for having the most important, best-preserved and extensive 'Pulham' garden in Wales, unusual in consisting partly of a highly elaborate underground network of grottoes and tunnels. The gardens, both above and below ground, were designed and built by the famous firm of James Pulham & Co, mostly using their trademark 'Pulhamite' artificial stone.

Overall, the gardens occupy about seven acres, and lie mainly to the west and south of the house. In their present form they were mostly laid out by Henry Oakley, who lived here from 1893 to 1940; it is likely that they were made from 1900 and completed by 1919. 

Immediately west of the house is a formal grass terrace and in the south-east corner of the terrace is the formal entrance to the underground gardens. They comprise a network of grottoes, or sunken chambers, linked by tunnels, passageways and winding paths, made from artificial rockwork, concrete, cement-coated brick and real stone. Decorative features built into the arrangement include dripstone pillars, stalactites, and arched doorways, with niches and planting beds for growing ferns. Water runs in over cascades into pools which are sometimes tiered, with islands and stepping stones, over waterfalls, and along winding streams crossed by bridges. Careful control over water flow is achieved with standpipes and water-cocks. Some sunken features had been infilled but were uncovered during recent restoration work. A further sunken, unroofed chamber was destroyed when a swimming pool was built. The chambers are thought to have been used for growing ferns in the numerous planting pockets. Some tunnels lead to former glasshouses. 

There are also extensive areas of rockwork above ground, complete with water chanels, pools and cascades in a mostly informal layout which included some formal elements (700081).

Sources:
Cadw 1994: Register of Parks and Gardens of Special Historic Interest in Wales: Gwent, 64-8 (ref: PGW (Gt)44(MON)).
Cadw Historic Assets Database.
RCAHMW air photos: 94-CS 1394; 945156/64.

RCAHMW, 6 April 2022