Pico Teide, Sendero de Montaña Blanca (Spain)
This is the fastest route to reach the top of Spain (3.718m), a track with 18 kilometers and 1.400 positive meters, from Montaña Blanca´s Parking to the top (ascent and descent by the same way to the parking).
There is a Strava segment for the ascent https://www.strava.com/segments/1272981 and for the descent: https://www.strava.com/segments/13234892