Arngerðareyri, often referred to as "Kastalinn" (the Castle), is a historic site located at the mouth of Ísafjörður in the Westfjords of Iceland. The prominent stone house, designed in a castle-like style, was constructed in 1929 for Sigurður Þórðarson, the manager of the Kaupfélag Nauteyrarhrepps trading company. Notably advanced for its time, the building featured six bedrooms, running water, a balcony, a water toilet, tiled floors, and marble stairs imported from Italy.

The site was abandoned in 1966. In 2012, new owners began gradual renovations to preserve the building. As of November 2023, the property was listed for sale, offering an opportunity for restoration enthusiasts to continue the preservation efforts.