The Negrón Tunnel (Spanish: Túnel del Negrón) is an automotive tunnel which connects the provinces of Asturias and León in Northern Spain. The tunnel is 4,144 metres (13,596 ft) long and reaches a height of 1,229 metres (4,032 ft). The tunnel is in the toll highway AP-66, which is part of the Autovía A-66, one of the longest highways in Spain. The tunnel provides an alternate route to the Puerto de Pajares, a mountain pass that is considered dangerous for motorists.