The Isle of Purbeck in Dorset, England - a peninsula rather than a true island, it has its eastern boundary along the coast at Studland and is bordered to the north by Poole Harbour and the flood plaints of the river Frome. The western boundary is less certain, but most likely placed at the western edge of Worbarrow Bay. The 96-mile long Purbeck section is arguably the most picturesque stretch.  

Purbeck  is the source of the grey shelly limestone, known as a Purbeck marble, from which the castle and nearby houses were built. The geology changes to the south-west at Kimmeridge, where the muddy shale is rich is fossils and oil reserves.

The main resort in the area is Swanage, the port where Purbeck stone was transported by ship to London. Unwanted masonry from demolished buildings was shipped back, and this is how Swanage got its ornate town hall façade, designed by Wren around 1668.

A large part of the area is a designed Area of Outstanding Natural Beauty with some of the coast owned by Ministry of Defence. The area was first requestioned during World War II for training exercises in preparation for the D-Day landings and is still used as a training area today, with live firing taking place on the ranges.