The edifice sits on 8,000 square feet, is laid out in a Latin cross with three naves each measuring about 100 feet in length and a transept with three naves measuring around 70 feet in length. The central nave is 22 meters high from floor to ceiling and rises to a peak of 32 meters in the transept's vault. The Gothic dome that now sits atop the transept's central apse replaced an older Romanesque structure.

The Romanesque ambulatory features a number of apsidal chapels, including a central chapel that is square in plan and two apses in each transept arm. A triforium with a quarter-barrel roof and a balcony with double-arched windows sits above the side naves, which are divided from the central nave by forty-two columns. There is a groin vault over the center nave and a barrel vault over the side naves.

Romanesque windows on the upper two levels of the side naves provide natural light; the main chapel's windows are multi-lobed, while the ambulatory's windows are portholes. The gallery's plant motifs and the ap's historiated capitals make up the interior decorating.

Both of the cathedral's massive organs may be found in the main nave's upper tiers, right in the middle. The cathedral chapter commissioned the master builder Manuel de la Via in 1708 and the case in 1712 from the architects Antonio Afonsn and Manuel Romay. In 1978, an Italian firm combined them, updated the console, and added electronic and computer mechanisms.