St Mary's Well Bay is a small bay backed by unstable cliffs and a holiday park. The upper part of the beach is pebbles and some coarse sand with seaweed covered rocks lower down. At low tide a sandbar runs parallel to the main beach and extends towards Sully Island. The beach looks out towards the islands of Steep Holm and Flat Holm.
Roadside parking is available on Fort Road (a no-through road off the B4267) just before the entrance to Marconi Holiday Park. The coast path westwards leaves the road here, passing through Lavernock Point nature reserve. A little further on are the remains of some substantial WW2 gun batteries and a useful information board to explain their history. The ruins of Lavernock Fort lookout post overlooks the bay and a short but steep, rugged path down to the shore is just beyond.