The town of Berchiddeddu was formed in 1800
from the union of three nearby farm-holdings and lies just 15 km from Olbia. The surrounding countryside abounds in springs which form streams where visitors can enjoy trout and eel fishing. Most of these streams flow into the "Rio Sa Castanza" and the "Rio Sos Campittos".

The Church of San Tommaso (Santu Tummeu) is of particular historical interest and dates back to 1500-1600. The facade presents a rectangular door with a plain architrave, with neither inscriptions nor decorations. Above the architrave there is a rose window, known as "Santa Caterina", with a diameter of 0.80 metres and stylised floral motifs which form a Greek cross. The roof is supported by juniper trunks and on the three altars there are images of the Patron Saint, San Narciso (Santu Narzisu) and the guardian angel (l'Agnulu di la gualdia).

However, this church is famous above all because it was once a sanctuary for exiles.
This privilege meant that it was in a position to grant immunity to those sought by the law who had taken refuge within its walls.
The church is surrounded by olive trees and secular oaks and a majestic holm-oak tree with a trunk circumference of 3.4 metres rises up from the square in front of the church. Not far from the church there is a pile of stones which, according to tradition, are the remains of a church which was erected in honour of Santa Giusta, virgin and martyr of Sardinia.

The Festival of San Tommaso is celebrated every year on the third Sunday in May and attracts numerous faithful to Berchiddeddu. The celebrations last for three days and are inaugurated with the arrival of the flags from the nearby towns. The flags are blessed by the parish priest and are then carried in procession around the church of Berchiddeddu (built in 1870) three times before being carried to the church of San Tommaso.

Another aspect which characterises the festival is the traditional communal lunch of lamb and boiled veal, which is offered to all the participants. The celebrations finish on Monday evening with the return of the flags to the church of Berchiddeddu, where the local people continue to celebrate far into the night.