Durdle Door (sometimes written Durdle Dor) is a natural limestone arch on the Jurassic Coast near Lulworth in Dorset, England. It is privately owned by the Welds, a family who owns 12,000 acres in Dorset in the name of the Lulworth Estate. It is open to the public. The name Durdle is derived from the Old English 'thirl' meaning bore or drill.