Orø Church Choir and nave of Orø Church have been built in late Roman style using boulders cut like ashlar blocks at corners and in doorways. Windows are framed with limestone and large bricks.
The two semicircular arched doors are preserved – the northern door has been walled up. Eight original windows can still be seen in the brick walls, all slightly pointed, suggesting that the church was built in the late 12th century.The belfry was erected at the beginning of the 16th century, along with the porch and the vestry. The repair of the church at the end of the 19th century proved somewhat ham-handed – two Roman windows in the northern wall were destroyed.
The Roman choir arch is preserved with a limestone string course. At the end of the 15th century cross vaults were built in both choir and nave, all piers having double string courses. At the restoration of the floor, fragments of glazed slabs with a rosette pattern were found. The altarpiece is from the Renaissance, related to the altarpiece in the church in Strø. The pulpit was made in 1632 and carries the arms of the noble families of Urne and Arenfeldt – the sounding board carries the initials of King Christian IV. At the northern wall of the nave a Pietá group can be seen – it is probably from around AD 1450. The choir arch crucifix, including side figures, from around 1500 has been placed where it originally belonged, above the choir arch. John the Apostle carries a girdle book in his right hand.
In 2001 covered murals were found on the northern and on the southern walls when limewashing the church. They have been uncovered along with the decorative ribs of the vault. On the northern wall a horseman can be seen, possibly Saint George – the illustration was partly destroyed in the restoration in 1897 when the Roman windows were enlarged. On the southern wall there is an angel, possibly from a depiction of the Annunciation, in that case Virgin Mary must be somewhere behind the wall pillar. The two murals and the rib decoration of the vault have been cleansed and restored without adding much paint.
The Orø Cross (also known as the Margrethe Cross after the finder) is a so-called reliquary cross, a breast cross to be worn in a chain around the neck, designed in two halves with a little hollow space in the middle. The shape is that of a Latin cross. At the front part the crucified Christ appears – he is stepping on the dragon of heathenism. Above his head, between the sun and the moon, we see the Lord´s right hand, and to the left and the right of Jesus´ arms two small figures, probably Virgin Mary and John the Baptist. The crossbar displays the letters OLAFC VNVnCE (Olav cununce = king) and ISACO' (possibly Isaac). The cross is from around AD 1100 and was found on Orø in 1849. Cross and chain consist of 310 g 22-carat gold. The cross is 8.3 cm tall and 6.25 cm wide. The original is kept at the National Museum in Copenhagen, but a replica can be seen at the museum Ourø Minder, Bygaden 56 on Orø.
At the back we see Virgin Mary wearing a veil and carrying an evangelistary. Above her head hovers the symbol of the Annunciation: the dove of the Holy Spirit and the letters S MA (Sancta Maria?). At the sides in medallions there are two saints and the Greek letters A and ? referring to Christ as the beginning of life as well as of the end.
The interior of the cross is empty, but there has probably been a reliquary holder, perhaps a splinter from the Cross, as in the Roskilde Cross (Danish text).