The Green Bridge of Wales is a natural limestone arch on the Castlemartin Peninsula, and its scale is surprising even when you know it's coming, a full arch of rock spanning out over the sea, worn smooth by millennia of Atlantic waves. It's the finest coastal rock formation in Wales.
Access requires crossing through the Castlemartin MoD firing range, which is only open on certain days, check before visiting. The walk to the viewpoint from the car park takes about ten minutes and is entirely worth the effort.