The optional undercliff Path runs 8.5 miles from Seaton to Lyme Regis and is graded moderate. Starting from Seaton after a short transfer, this section begins at the peaceful River Axe Estuary, crossing the historic Old Toll Bridge. The walk then enters the extraordinary Downlands Undercliff, a National Nature Reserve created after the dramatic 1839 landslip, which formed a jungle-like, untouched ecosystem. Locals once witnessed a huge part of the coastline slip into the sea, creating a new island called Goat Island. The path winds through dense undergrowth, home to over 80 bird species and wildlife such as badgers, foxes, and roe deer. The terrain is wild and rarely disturbed by humans, with lush vegetation and occasional views of the rugged coastline below. The trail eventually climbs out of the undercliff, offering expansive views towards Golden Cap and the Isle of Portland, before descending into Lyme Regis and its historic Cob Harbour, marking the start of Dorset on the South West Coast Path.