Where was Heartstone filmed?
2016 film by Guðmundur Arnar Guðmundsson
Heartstone (2016) was filmed in Seyðisfjörður, Vopnafjörður, Dyrhólaey and Borgarfjörður Eystri, 4 places named in its Wikipedia article's Production section, in Iceland. Wikidata records no filming location for it at all, so the article is the only recorded source. Each place says where its claim comes from.
Places per Wikipedia's Production section
Wikipedia’s Production section names 4 places. Each links to the sentence that says so.

