Xin'an, also known as Nantou Ancient City, preserves the site of the old county town that once governed the area around modern Shenzhen and Hong Kong. Much of the district has been rebuilt, but the Ming-era gate and wall, Guan Yu Temple, old official buildings, and dense lanes still give it a strong historic texture.
It is best visited as a slow walk through Nanshan rather than as a museum stop. Look for the small archaeological museum near the south-west side of the old town if you want more context.