N623 is a spectacular national Spanish road with a total lenght of 160 km, between the cities of Burgos and Santander.
The road, which reaches several mountain passes, goes through the regions of Castilla León and Cantabria, with spectacular scenarios, and many hairpins.. N623 is a two lane highway, totally asphalted and with guardrails.
It starts at Burgos on the Autovía A-62 and a junction with N-I. It passes through the city over the River Arlanzon. It then heads north having a junction with the N-627.
The road then climbs to cross the Puerto del Paramo de Masa and then Portillo del Fresno (1,050 m). The road then winds down to the Upper Ebro valley. There is a junction with the N-232 at the eastern edge of the Embalse del Ebro. The road then climbs again into the Cordillera Cantabria crossing Puerto del Escudo (1,100m). 
Continuing along a narrow valley the road reaches the N-634. Thereafter, the road turns north east towards Santander and a junction with the Autovía A-67.
