[3] Grassy clearings within the combe are the only site in Avon where the nationally scarce Spreading Bellflower Campanula patula is found.

[4] Harptree Combe is a narrow limestone gorge containing a variety of habitats, including Ash woodland, rough grassland, natural and artificial rock faces, and a small, marshy stream.

The limestone rock exposures and aqueduct walls are location for many species of moss and fern, some of which, e.g. Rusty Beard-moss Didymodon ferrugineus (previously Barbula reflexa), Brown Beard-moss Didymodon spadiceus (previously Barbula spadicea) and Brittle Bladder-fern Cystopteris fragilis, are rare in Southern England.

It consists of a wrought iron tube, which runs underground for 18 kilometres (11 mi), to Bristol Reservoirs but where it appears above ground it is supported by limestone piers and abutments.

In 1138 it was strongly garrisoned by its owner, William de Harptree, on behalf of the Empress Matilda, but was taken by Stephen by the ruse of a feigned repulse.