Holyhead, on the island of Angelsey, which lies off the northwest coast of Wales, in the eighteenth century had developed into the major port linking Ireland and the British Isles. It was the closest landing place to Dublin, with some 100 kilometers of the Irish Sea intervening. Since, however, Anglesey was an island, passengers still had to negotiate the treacherous Menai Strait linking it to the mainland. In 1810 Thomas Telford was commissioned at this site to build the first suspension bridge in the world as part of a modernization of the coach road to Holyhead.
Mary Shelley never traced this itinerary, but Percy did, both going to and returning from his Dublin adventure via Holyhead in 1812. Mary Wollstonecraft had also taken this route when she took up her post as governess in the Irish seat of Lord and Lady Kingsborough in 1786.