Most visitors to Kalambaka rush straight past this Byzantine cathedral on their way to the monasteries, which is a mistake. The Cathedral of the Assumption of Mary dates to the 11th century, built on the foundations of a 5th-century early Christian basilica. The carved marble ambo (pulpit) in the interior is considered one of the finest examples of early Christian stonework in Thessaly.
The frescoes inside span several centuries, with the oldest sections dating from the 12th and 13th centuries. The apse mosaic of Christ Pantocrator has survived in good condition and is worth the short detour from the main square. The church is usually open in the mornings and provides a cool, shaded retreat during the heat of the day. Admission is free, though a small donation is appreciated.