The penultimate stage features the second of two hors categorie summit finishes, where – despite there still being a time trial to come – the race could be won or lost.
The flat, ten-kilometre time trial circuit around Santiago de Compostella on the final day could allow some riders to claw back seconds overall, but the real final gains are likely to made on the Puerto de Ancares on stage 20.
One of five climbs on the route for stage 20, the final summit finish follows the category-one Alto de Folgueiras de Aigas, meaning it is likely to be a select lead group contesting the summit finish.
Its steepest sections feature early in the climb, with one ramp in particular touching 18 per cent in gradient.
By comparison, the climb flattens somewhat after nine kilometres or so, becoming more of a long, straight drag before kicking up again for the final 2,000 metres or so.
Depending on the overall situation, expect attacks aplenty – with Alberto Contador hoping to be on top form come the final few stages, and the likes of Nairo Quintana and Rigoberto Uran looking to prove their climbing supremacy.
Giro d’Italia King of the Mountains winner Julian Arredondo is another Colombian who could well be in contention for the stage.