Castor Hanglands is an 89.8-hectare (222-acre) biological Site of Special Scientific Interest west of Peterborough in Cambridgeshire.

[6] The location features ancient ash and maple woodland, unimproved grassland and scrub, and is further described by Natural England as valuable for invertebrates, including some nationally uncommon species.

Among the rare plants found here are crested cow-wheat, lesser water-plantain, man orchid and narrow-leaved water dropwort.

Woodland butterflies present include silver-washed fritillary, purple hairstreak and white admiral.

[8] There is access by going south along Heath Road from Helpston, going straight on at the crossroads and then along a track westward to the reserve.