If a HNI (High net worth individual) buys an island on a different country for which the individual doesn't has a nationality/citizenship , then does the individual has to take a separate visa for entering his/her own island via waterways (reaching to the nearest point by cruise & then taking a boat ⛵ to reach the island 🏝️) , without actually entering the mainland ?
Note :- This isn't a country specific question , so any examples & counter-examples would do the job.