Hola @nathanael ; yes there is an alternate track/trail/route but it is mainly for those on bikes. From Castro take the main road (BU400) north for about 3.5 km till your reach Castrillo de Matajudios; then turn west onto the BU403; follow this road for about 6.5 km to Itero del Castillo or another 2 km over the rio Pissuerga to Itero de la Verga. So about 12 km as opposed to 11 km up the big hill.
Just for reference - I rode & walked the hill in 2015 and it took over 45 mins; in May last year, admittedly a lot cooler and greener it took less than 30 mins from the bridge over the rio Odrilla. (these roads are shown on Brierley but are unnamed) nor is the little village Matajudios!
Hope this helps!!
as Mike has said, there is a route around but my hope is you will take the hill unless there is a physical reason it is not possible. These physical challenges provide opportunities to stretch and build ourselves and through these challenges find out just how strong we are and how much we are capable of! Ultreia!!