At first sight, it looks like a normal single-nave church, without friezes or external decorations, built in the courtyard of the Serravalle Castle in Bosa, a picturesque medieval village in the Planargia region. In reality, the church of Nostra Signora de sos Regnos Altos hid its priceless wealth in the internal walls, under the plaster. ...and it may still be jealously guarding some secrets. One is linked to its founding, with no source, so the theories formulated vary between the 12th and 14th centuries. Subsequent renovations, also undocumented, fuel the mystery. The church probably served as a palace chapel inside the castle. It has a rectangular hall with a semicircular apse and two entrances, one on the façade and one on the north-east side. At the end of the 19th century, a decision was made to extend the hall to the east and this involved the destruction of the original apse. The great revelation, however, came to light during the consolidation works in the two-year period of 1972-73: while removing the plaster, a surprising series of frescoes appeared, which had originally occupied the entire perimeter of the building and are interrupted on the eastern side due to demolition of the ancient apse.