Members of Manx National Heritage and the National Trust of Guernsey will be eligible for free entry to sites in both jurisidctions.
It comes following the two charities reaching an agreement ahead of an 'air bridge' which allows flights between the two Islands later this month.
Manx visitors will be able to go to the Folk and Costume Museum at Saumarez Park, and the mid-19th-century Les Caches Farm.
Meanwhile, members from Guernsey will be able to visit eight sites here for free, including the likes of Castle Rushen and the house of Manannan.
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