Peñafiel Castle is built with stone from Campaspero and is an example of Germanic Gothic. It measures 210 metres long, and 33 wide.
This castle is situated on a hill from where it is possible to see the Duratón and Botijas valleys. Its outward appearance is smooth and it has only one gateway. The plan of the keep is rectangular, it measures over 30 metres high and 14.5 by 20 at the base, and is topped by eight small towers. The keep is flanked by two courtyards. The interior of the castle has two floors with a stone vault. It was declared a National Monument in 1917.