If you want the beach over Florence or Lucca then Viareggio is probably a good choice. It is a resort town (fairly large at that) and, as such, attracts tourists from all over Europe (as well as some cruise passengers.) You C/L excursion will get you admittance to a private 'club' and probably will include your own beach chair (nope, you cannot move it.) They are funny that way - all lined up in neat rows aligned exactly the way that they want them. It's a Mediterranean beach club so enjoy it for what it is.
For grins, go to maps.google.com and search for 'viareggio, it'
Use the zoom slider to move in closer (you may have to move left/right to keep beach centered.) As you get closer you will see all of the beach chairs lined up.
Radiance of the Seas - Nov 2006
Legend of the Seas - Jun 2007
Costa Fortuna - Mar 2008
Legend of the Seas - Oct 2008
Celebrity Constellation - July 2009
MSC Orchestra - Jan 2009
Navigator of the Seas - March 2009
MSC Poesia - November 2009
Jewel of the Seas - June 2010