Sandtop Bay is a secluded sandy beach on the west side of Caldey Island. Although there is now an extended coastal path to the south-western side of the island there is no official access to the beach itself.
The beach consists of coarse sand, backed by a bank of blown sand which is covered in marram grass and a sprinkling of sea holly, with a faint path down at the north-eastern corner. The limestone cliffs on the north side of the beach are almost vertical, while on the south side the cliffs are of red sandstone. The beach looks out towards the island of St Margarets and Old Castle Head. The steeply shelving beach and unpredictable currents make swimming and even paddling dangerous, and there have been drownings here.
Landing on the island (apart from the official boats from Tenby) is not allowed. St Margaret's Island, to the west of Caldey is managed as a nature reserve and is linked to Caldey by a low-tide causeway. Reaching it is difficult, and attempting to cross is dangerous.