The present cathedral has two principal altars. The one in the octagon at the east end of the chancel rests on the site of the medieval high altar which bore the silver reliquary casket containing the remains of St. Olav,[1] the church’s and the kingdom’s patron saint, and is designed to recall in marble sculpture the essential form of this reliquary casket. It replaces the previous baroque altar presently in Vår Frue Church. The second altar is in the crossing where the transept intersect the nave and the chancel. It bears a large modern silver crucifix inspired by the memory of a similar silver crucifix in the medieval church and was commissioned and paid for by Norwegian American emigrants in the early twentieth century. The medieval chapter house may also be used as a chapel for smaller groups of worshipers.
en.wikipedia.org/wiki/Nidaros_Cathedral