Sail to discover those magic islands
Sail - here it means, travel by ship on or across (a sea).
How grammatical the use of the word "sail" here? (even if we think little poetically)
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"Sail away and discover those magical islands."
Is that what you want? Your usage of "Sail to" in your example is troubling.
[FWIW I've said this before elsewhere, sorry - but as a learner you will do well to stick to what you hear said in its specific context].