Recommend visiting all the ships and the lighthouse.
Depend on the situation... how many ships do you want to visit.
When I went you didn't have the option to choose just one ship
$15 gives you the option of two ships. $18 for 4 ships. I can't remember the cost for a single ship.
Its about $20 for the full set It included 4 ships. It may change depending on tourist season I am unsure of that.
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