In Pastrana's historic district lies the Catholic temple known as the Collegiate Church of La Asunción. It has a museum with a sizable collection of tapestries as well as a variety of paintings, altars, gold and silver objects, and reliquaries, among other types of artwork.

The Calatravan knights' early Romanesque church from the 13th century, parts of which are still visible, served as the inspiration for the collegiate church of La Asunción. Although there are already improvements to the Romanesque church in the 14th or 15th century in the region of what is now the choir, it was entirely reformed in the 16th and 17th centuries. Moreover, a new gateway in the Gothic style with an ogee arch and two lateral pillars topped with pinnacles and fleurons was constructed on the north wall, the current entrance.

However, the first significant change occurred in 1569 when Ruy Gómez de Silva, the first Duke of Pastrana, secured the papal bull allowing the cathedral to be transformed into a collegiate church. He constructed a sizable Gothic-style chancel, maintaining the naves of what is now the choir without making any changes to them, to fit the structure to its new canonical position.

The building underwent a second significant alteration between 1626 and 1639 under the direction of Archbishop Pedro González de Mendoza. Alberto de la Madre de Dios, a Carmelite architect, was hired to complete the project. Following the classicist Escullian style, the church's chevet was replaced by a larger one with a crypt and transept. As a distinctive feature of the church and a byproduct of the 17th century reform, the height difference between the chancel and the remainder of the church is also preserved.

Large burial urns are housed in the crypt, which has a Latin cross floor plan. Six of the urns are constructed of pink marble from the ducal pantheon of the monastery of San Francisco de Guadalajara, and the remaining urns are built of granite from the crypt itself. With the exception of the bell tower, which the Modern Era regrettably attached a clock to, this is the temple's last significant renovation and the one that shaped its current design.

An major collection of Flemish tapestries is housed in the collegiate church's museum, whose growth in recent years has generated debate.

There are three series in the tapestry collection:

a group of four Flemish wool and silk tapestries that are believed to have been created at Tournai, Belgium, between 1472 and 1475 and show scenes from the Battle of Alcazarquivir.

The siege of Alcazarquivir and the entry into Alcazarquivir are shown in two further Flemish tapestries from another series that were created at the end of the 15th century and have similar war themes to the earlier ones.

Two tapestries from the Tetrarch series, which dates to the end of the 15th century and depicts numerous acts of Alexander the Great.

Josep Pascó's illustration of the college church (1886)

As a result, the church has three very wide naves that open into a massive transept at the chancel and are topped by a brief presbytery or main chapel. The complex is completed with several altars, chapels, and outbuildings.

Notable is the organ, which Domingo de Mendoza, the Royal Chapel's master during Felipe V's reign, built in 1704.