Oxwich Bay Dog Walk: Information
If you walk to the opposite end of the Bay from Oxwich Bay Hotel, you will come to a rocky promontary. At low tide you can skirt around this and continue your walk for another 30 minutes or so, along the next Bay, which is Three Cliffs Bay. Just be sure to watch the tide for the return journey.
If you do get stuck the Three Cliffs Bay end, you can find a path over the headland back to Oxwich Bay, though I have never had to do this.