The Sea-to-Sky Corridor, often referred to as the Corridor, or the Sea to Sky Country, is a region in British Columbia spreading from Horseshoe Bay through Whistler to the Pemberton Valley and sometimes beyond to include Birken and D'Arcy. From Whistler on up, the region overlaps with the older and more historic Lillooet Country, of which Squamish, at the region's centre, was once the southward extension in the days when it was the rail-port terminus from the Interior, via Lillooet, and accessible from the Lower Mainland only by sea. Most of the region is in the Squamish-Lillooet Regional District, although south of Brittania Beach a small part of the region is in the Greater Vancouver Regional District.