Botanical Gardens make a gorgeous venue for a wedding and St. Croix has the St. George Village Botanical Gardens which is a great place for your ceremony.

STANDARD WEDDING

Aboard a Boat certainly makes for a picturesque wedding ceremony.
Of course standard weddings are the most popular (especially when compared to underwater weddings).
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Just because I'm calling it "standard" doesn't mean it won't be special.  
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Whether your wedding party will be just the two of you (we need two witnesses but we can always find some), or a very large group you'll find a beautiful venue on St. Croix for it.
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Beachfront weddings are the most popular of course and there are a LOT of beautiful beaches surrounding St. Croix.