Grotto or shell house in the grounds of Thames Eyot

The grotto or shell house, likely dating to the 18th century, stands within the grounds of Thames Eyot. It is square internally, measuring approximately 2.3 metres by 2.3 metres and 2 metres high. The structure is built of brick, with a brick vault supported by low brick walls. It is partially concealed beneath a turf mound, resembling an ice house in scale and form, and there’s a suggestion it may be a remodelled ice house or a garden structure shown on an earlier view.

The grotto opens from the north-western end of a loggia. Initially, a wide, arched entrance constructed of dark red, purple, and grey brick opened to the south-east. This phase of decoration involved covering the vault and walls with a grotto-like finish. Later, the arch was partly in-filled with red-brown brick, creating a narrower entrance that appears asymmetrical from the outside, but is centrally placed when viewed from within. The roughly jointed arch suggests it was originally rendered or decorated, possibly indicating an earlier, simpler garden structure. The exterior southern wall, where not clad in stone, is faced with knapped flint.

The interior features a floor of accumulated earth and later 20th-century brick stub walls. The interior surfaces are decorated with shells, pebbles, coloured stone, slag, fragments of glass, and pottery. Approximately two-thirds of this decoration survives. The vault’s centre is designed as radiating spokes of small winkles extending from a central hub, with concentric rings of iron-coloured pebbles and flint, pink, red, and blue slag, set on a base of larger scallops. The vaulted ceiling is lined with panels resembling a coffered ceiling, following the shell house's profile, formed by vertical ribs of small scallops. Rectangular sections have a large scallop at the centre, surrounded by smaller scallops, pebbles and blue slag. The rear wall features a brown flint and pebble arch with a prominent keystone, enhanced below with pottery and glass fragments. A band of flint and slag marks the division between the vault and the walls. The side walls display a random scatter of flint, pebbles, slag, and circles and lozenges of buff and brown pebbles. The entrance wall’s inner face is lined with bands of blue slag and flint, extending to the outer wall surface.