Today at 12 pm (26th august 2019) entry tickets are available on the official website for the Caminito del Rey for the months of November, December and January
It is recommended to book now and well in advance, as tickets are often sold out online very quickly.The daily quota of visits every day is limited to 1,100 tickets for security reasons and to preserve the natural site.
At the online booking system you have the option of choosing a general self guide admission (10 euros) or the guided tour option that is available in both English and Spanish (18 euros)
Best of luck!
Official website for tickets is here.