...de la Sierra by bike. Olvera-Puerto Serrano. 37 km. Average difficulty. 15 euros including bus and bike hire. 26 November. El Chorro-Carratraca GR-249. 15 km. Average difficulty. 9 euros. 3 December. Roman road family walk. Benaocaz-Ubrique. 3.5 km. ... planned for 19 November to the green route of the Sierra de Olvera and Puerto Serrano. “The more activities created to promote the use of bikes, the better, whether for getting to know Marbella, or to get to other places,” stresses one organiser.