A total of £768,000 has been spent on Castle Rushen in the past 15 years.
The money's been spent on stone masonry, maintenance, restoration and conservation work.
The figure was revealed by Enterprise Minister Tim Johnston in response to a written Tynwald question from Arbory, Castletown and Malew MHK Jason Moorhouse.
Mr Moorhouse wanted to know whether Manx National Heritage had invested anything in the attraction's gift shop.
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