Earthworks in a field to the east of Trewyn House, consist of boundary banks, platforms, a holloway and a linear watercourse. A 'Chapel of St Martin at Trewyn' is listed in the Llanthony Priory estates records at Dissolution, though seventeenth and eighteenth century documents for the Trewyn estate do not mention a chapel, which probably indicates that it had fallen out of use by this stage.

An earthwork platform in the centre of the field, measuring 15 meters by 10 meters could be the site of the chapel. The Chapel may have functioned as a wayside chapel on a pilgrimage route associated with Llanthony Priory.
Source: Details extracted from Dissertation by Mr. E. Procter