The route leaves Tabernas and heads north into the Sierra de Los Filabres to Velefique. From there it climbs on the AL-3102 to join the summit roads and finishes at the Calar Alto Observatory. It uses the AL-3102, the A-1178, the AL-5407 and the AL-4404. It is a true mountain-pass route, going from semi-desert to high mountain in a few dozen kilometres.
It crosses the municipalities of Tabernas, Castro de Filabres, Velefique, Bacares and Gérgal. You start in the arid surroundings of Tabernas, with dry riverbeds and bare hills, and gain height up the side of Los Filabres through a series of tight hairpins above Velefique. Higher up the landscape opens out, with planted pine forest and very wide views. At the summit of Calar Alto stands the astronomical observatory, one of the leading centres for astronomy in Spain.
It is about 63 km and the estimated time is around two and a half hours without stops, reflecting how twisty it is. Altitude ranges from around 400 m to around 2,150 m, a very large climb: the temperature at the top can be much lower than in Tabernas. There are hardly any services in the sierra, so set off with a full tank. Watch for gravel on bends, livestock and cyclists, who are common on this climb.