Nassau is the most-visited port in the Caribbean and the one people most often write off. It is worth understanding why before deciding what to do with the day: the ships dock in the middle of a working capital city of a quarter of a million people, and the four blocks immediately around the pier are given over to duty-free jewelry shops that have nothing to do with the Bahamas.
Walk past the first four blocks. Ten minutes east and uphill puts you at the Queen’s Staircase, sixty-six steps cut by hand through solid limestone, and Fort Fincastle above it. Ten minutes west puts you on Junkanoo Beach, which is free, public and perfectly decent.
The good water is a boat ride away. New Providence’s own beaches are fine; the postcard water is at Rose Island, Blue Lagoon or the sandbars, all half an hour out by boat. If the point of the day is the sea, book something that leaves the island.
Atlantis is a day pass, not a stroll. The resort on Paradise Island sells water-park access by the day and it is not cheap. It is a good day with children and a poor one without.
Cash is unnecessary. The Bahamian dollar is pegged to the US dollar and the two circulate interchangeably; you will get change in a mix of both.