Question: What river goes by the oldest continuously occupied castle on mainland Scotland?
Context: The Saltford Manor is a stone house in Saltford, Somerset, near Bath, that is thought to be the oldest continuously occupied private house in England, and has been designated as a Grade II* listed building. Ximenez-Fatio House Museum is one of the best-preserved and most authentic Second Spanish Period (1783-1821) residential buildings in St. Augustine, Florida.  In 1973, it was added to the National Register of Historic Places.  It was designated a Florida Heritage Landmark in 2012.  The museum complex sits just south of the city's central Plaza de la Constitución at 20 Aviles Street (formerly Hospital Street), the oldest archaeologically documented street in the United States.  It is located at the center of Old Town, the city's oldest continuously occupied community.  Since 1939, the property has been privately owned and managed by The National Society of The Colonial Dames of America in The State of Florida (NSCDA-FL).  Through their efforts, it was restored and interpreted to reflect its function as a fashionable boarding house during Florida's first tourist boom, which began after 1821.  The property is a historic house museum, furnished and presented to tell stories of the visitors who lodged there, the women who owned and managed it, and how people lived during Florida's territorial period. This is a list of Orkney islands in Scotland.  The Orkney archipelago is located 16 km north of mainland Scotland and comprises over 70 islands and skerries, of which 20 are permanently inhabited.  In addition to the Orkney Mainland there are three groups of islands.  The North and South Isles lie respectively north and south of Mainland.  The Pentland Skerries are a group of small islands in the Pentland Firth, a dangerous stretch of water between mainland Scotland and the larger islands of Orkney, through which run the strongest tidal streams in Britain.  The Isle of Stroma is often mistakenly included with the Orkney Islands, but is part of Caithness. The Palace of the Governors (1610) is an adobe structure located on Palace Avenue on the Plaza of Santa Fe, New Mexico, between Lincoln Avenue and Washington Avenue.  It is within the Santa Fe Historic District and it served as the seat of government for the state of New Mexico for centuries.  The Palace of the Governors is the oldest continuously occupied public building in the United States. St. Thomas Manor (1741) is a historic home and Catholic church complex located near Port Tobacco, Charles County, Maryland.  Today, the manor house complex is recognized as the oldest Jesuit residence in the world to have been continuously occupied by that order.  The mission settlement of Chapel Point was started in 1641 by Father Andrew White, S.J., an English Jesuit missionary.  He administered to the Potapoco Native Americans, some of whom he converted to Catholicism.  Established in 1662, this is the oldest continuously active Roman Catholic parish in the Thirteen Colonies of North America founded by Great Britain.  With the consecration in 1794 of Bishop John Carroll, St. Thomas became the first Roman Catholic see in the United States. West Point is the oldest continuously occupied military post in the United States.  West Point was established in 1775 by George Washington who considered it the most important strategic position in America.  Until January 1778, West Point was not occupied by the military.  On January 27, 1778, Brigadier General Samuel Holden Parsons and his brigade crossed the ice on the Hudson River and climbed to the plain on West Point and from that day to the present, West Point has been occupied by the United States Army.  It comprises approximately 16000 acre including the campus of the United States Military Academy at West Point, which is also frequently called "West Point".  It is a Census Designated Place (CDP) located in the Town of Highlands in Orange County, New York, located on the western bank of the Hudson River.  The population was 6,763 at the 2010 census.  It is part of the New York–Newark–Jersey City, NY–NJ–PA Metropolitan Statistical Area as well as the larger New York–Newark, NY–NJ–CT–PA Combined Statistical Area. Duntrune Castle is located on the north side of Loch Crinan and across from the village of Crinan in Argyll, Scotland.  It is thought to be the oldest continuously occupied castle on mainland Scotland.  The castle is a category B listed building. Scoles Manor, also known as Scoles Farm House, is former farmhouse and a Grade II* listed building, two miles from Corfe Castle in Dorset, England.  It is believed to be the oldest continuously occupied building in Corfe Castle parish.  The main part of the house was built in 1635 and there is a medieval structure attached which has been dated to 1280 and which was either a chapel or a small hall house. The history of St. Augustine, Florida, the oldest continuously occupied settlement of European origin in the United States, began in 1565 when it was founded by the Spanish admiral, Pedro Menéndez de Avilés.  The Spanish Crown issued an "asiento" to Menéndez, signed by King Philip II on March 20, 1565, granting him various titles, including that of "adelantado" of Florida, and expansive privileges to exploit the lands in the vast territory of Spanish Florida, called "La Florida" by the Spaniards.  This contract directed Menéndez to explore the region's Atlantic coast and report on its features, with the object of finding a suitable location to establish a permanent colony from which the Spanish treasure fleet could be defended and Spain's claimed territories in North America protected against incursions by other European powers. Loch Crinan is a seawater loch on the West of Scotland, leading into the Sound of Jura and being the western end of the Crinan Canal.  The village of Crinan is at the entrance to the canal at the eastern end of the loch.  Duntrune Castle stands on the northern shore.  The River Add goes into it by the hamlet of Bellanoch.
Answer: River Add