The tombolo is an uncommon natural feature where a sandbar connects two separate landforms over water. In the Shetland Islands, tombolos are among the best-known natural attractions, especially since, as in the case of St Ninian's Beach, they often feature powdery, light-colored sand and turquoise waters, making them look as though they are two tropical beaches stuck back-to-back.

The tombolo-like formations in Swinister may not be Caribbean-like, but they make up for it in quantity. The word ayres is normally reserved for shingle beaches, whereas the tombolos are sandy. The Ayres of Swinister are mostly shingle, but sand can be occasionally found on some of its beaches. Despite the prevalence of both tombolos and ayres in Shetland, Swinister's are special since they form a single, full tombolo connection between the island and mainland, along with two others that come close.

Perhaps the world's most famous double tombolo, or at least the one most widely recognized as such, is the peninsula of Giens in France. Given Swinister's second and third features protruding towards the island, despite not forming a full connection, it could be considered an almost-triple tombolo, which may make it one-of-a-kind.