An historic island fortress has been put up for sale with a guide price of £6 million.
Drake's Island in Devon includes a 16th century barracks, a pier and an underground network of tunnels.
The six-acre site, which stands 600m off the coast at Plymouth, has planning permission for a luxury hotel and spa.
Aidan McCauley, son of the island's owner Dan McCauley, said: "My dad has long held a vision to see the island brought back into use.
"We are passionate about seeing his vision turned into a reality and are exploring all options to make this happen."
The island was named after Sir Francis Drake, who set sail from there in 1577 to circumnavigate the globe.
The fort played a crucial role in the defending the maritime city from French and Spanish invasions in the late 16th century and has been used as a prison, a religious centre, a refuge and, most recently, an adventure training facility, which closed in 1989.
Mr McCauley, a businessman and former chairman of Plymouth Argyle football club, purchased Drake's Island in the 1990s.
In spring 2017, Plymouth City Council granted planning permission to create a luxury hotel complex including the conversion of the existing buildings.
John Kinsey from property agent JLL said: "Drake's Island is a remarkable piece of British history and a much-loved landmark.
"With the added attraction of planning permission for a luxury hotel and spa this is a unique opportunity to lead one of the South West's most exciting and unusual developments."