A stone arc built out into the sea, almost enclosing a lagoon. There's nothing built on the island yet, just the shape itself.
Halfmoon isn't a natural island: it was built up with fill. The rock fill runs in an arc that almost closes into a ring, leaving a passage inside. Inside is a lagoon, whose water is noticeably lighter than the open sea.
The island is linked to shore by a causeway of fill. At the eastern end of the arc there's a separate round islet.
