Since the early 21st century the island has been developed as a heritage tourist attraction,[4] with €5.5 million investment in exhibition and visitor spaces[5] and accompanying tourism marketing.

[9] The principal evidence for a monastic foundation on Spike Island comes from Archdall's Monasticon Hibernicum,[3][10] which states that Saint Mochuda founded a monastery there in the 7th century.

[11] The grant to St Thomas's abbey in 1178 coincides with the surrender of lands, including Spike Island, by Diarmid McCarthy King of Desmond to the Normans.

In 1698, the island was in the possession of Arnold Joost van Keppel 1st Earl of Albemarle who had accompanied William of Orange to England in 1688.

[13] It would seem that the government leased part of the island for fortifications in the 1770s while the owner remained in residence - the house only being demolished during the construction of the present fort.

The Spike Island Battery was a temporary work and armed with eighteen 24 pounder cannon moved from Cobh Fort.

[15] In 1802, General John Hope, 4th Earl of Hopetoun recommended that a major fortress be constructed on Spike Island, capable of holding 2,000-3,000 men.

Lieutenant General David Dundas was consulted by the Duke of York, Commander in Chief, who also recommended that a fortress should be erected on Spike Island.

It was the job of this board to implement the decision to erect the fortress and it fell to Charles Holloway, Commanding Engineer Cork District, to begin the works.

[15] In 1804, the Hampshire Chronicle reported that the overall height of Spike island had been reduced by 25 feet and the spoil used as infill to create a level foundation.

[4][21] Spike Island was home to Ellen (Nellie) Organ who gained special permission to take First Communion shortly before her death at the age of 4.

Certain mooring buoys to be retained for use of His Majesty's ships.Accordingly, even after the establishment of the Irish Free State, the Royal Navy continued to maintain its presence at Spike Island.

Spike Island remained under British sovereignty until 11 July 1938 when pursuant to the Anglo-Irish Trade Agreement of 25 April 1938, the territory was ceded to Ireland.

The handover ceremonies were attended by senior military and political figures, including Éamon de Valera and Frank Aiken.

)[26] The island remained the site of a prison and military base (for the regular Irish Army, the FCÁ and later the Navy) for some time.

In 2009 it was announced that ownership of the island would be transferred (free of charge) to Cork County Council to enable its development as a tourist attraction.

Since 2015, tours depart from Cobh during the summer,[30] taking in the fort, prison cells, gun emplacements, and key points of interest.

[5][33] As well as the previously opened buildings and 6-inch gun emplacements, as of Summer 2016, visitors to the "Fortress Spike Island" cultural heritage attraction can also tour the "punishment block", the 1980s cells (which include an exhibition on the 1985 Spike Island riot),[34] the recreation of the hull of a "transportation ship",[35] and an interpretative installation on John Mitchel - for whom the fort is named.