Don't forget to visit Queen's Staircase and Fort Fincastle on your walking tour of Nassau. My son loved both. There's a wonderful view of the harbor from atop the fort.
Last year we went to Cable Beach (you don't have to pay for beach access - the resorts are MORE than happy to let you walk thru the front door and hopefully buy from the beach vendors and drink at their beach bars) and parasailed. Not for the faint of heart, but I sure am glad we did!
Cabs really are fine in both ports. They ferry about a LOT of cruise ship passengers and I've always felt perfectly safe. I too sailed with my son alone - for his 13th birthday.
We did the glass bottom boat trip and he really enjoyed it, too.
CarnivalSensation February 2015
Carnival Dream November 2015
Carnival Fascination April 2014
Carnival Elation March 2011
Carnival Imagination Sept 2007
Carnival Sensation Dec 2006
RCI Sovereign of the Seas Sept 2006
Carnival Miracle Sept 2005
Carnival Glory Sept 2004
Carnival Fantasy Jan 2004