The tunnel is constructed from brick with walls thick, faced with
Hamstone. It runs for under Horn Hill, a promontory to the north of Beaminster. The hill presented a major barrier to travellers passing from the newly enlarged harbour at
West Bay on the Dorset coast to the hinterland; according to a contemporary writer, the hill was "a great impediment to the communication between the lower portion of Dorsetshire and a considerable district of Somerset, particularly with regard to
Bridport harbour." The main road passed over the hill, climbing almost 500 feet in a mile-and-a-half (150 metres in two kilometres). The steep gradient of 1-in-6 (17%) made passage difficult for horse-drawn transport. In the late 1820s, a Beaminster solicitor named Giles Russell proposed that the owners of the toll road over the hill, the Bridport 2nd District Turnpike Trust, should seek to build a tunnel under it to shorten and flatten the road. Russell played a key role in getting the project underway and managed to raise the £13,000 required through loans and contributions from many of Beaminster's artisans and traders.
Opening The tunnel was formally opened on 29 June 1832 with enthusiastic celebrations including a
21-gun salute fired from the top of the hill, a firework display and the launching of a
hot air balloon. A procession of dignitaries, local people and the tunnel workers paraded through the tunnel accompanied by three flag-bearers, two bands, the project's patron in a four-horse open carriage and the Commissioners of the Trust and various officials in a mail wagon. A celebratory dinner was held afterwards in the White Hart inn in Beaminster, where Giles Russell was the guest of honour. A song was especially written for the occasion, including the lyrics: The yielding soil, through able hands, A tunnel wide displays; And Lane’s efficient aid demands Our warm, admiring praise In swelling streams may cheering wealth To Beaminster descend: And ever joy-inspiring health Her social sons attend. Commemorations of the opening of the tunnel became an annual tradition in Beaminster with "Tunnel Fairs" being held every Good Friday on Horn Hill until about the 1880s. In 1881, the tunnel became free to use when the tollgates were removed and the toll house at the north end was converted into a dwelling for the tunnel's lamplighter. The house was later demolished to allow the road to be widened. The two entrance portals are
Grade II listed as being of Special Architectural or Historic Interest. ==Renovation and repairs==