Boston Lodge is situated at Penrhyn Isa, Minffordd, Penrhyndeudraeth, on the A487 road about 1 mile SE across the Afon Glaslyn causeway from Porthmadog, Gwynedd in north-west Wales. It has a station on the Ffestiniog Railway and is the location of the railway's main engineering workshops, locomotive shed and carriage works. The Boston Lodge address and postcode is shared by the works with four cottage dwellings (mostly occupied in connection with the railway) and with the former tollgate cottage at the end of the causeway. The original 'Penrhyn Isa' cottage (now the railway works office) was renamed 'Boston Lodge' after Boston, Lincolnshire, the parliamentary seat of William Madocks, the proprietor of the land reclamation venture.