Where was SKY Castle filmed?
2018-2019 South Korean television series
SKY Castle (2018–) was filmed in Yongin, 1 place named in its Wikipedia article's Filming section, in South Korea. 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 Filming section
Wikipedia’s Filming section names 1 place. Each links to the sentence that says so.