Hi, Sandi ...
Just jump off the ship at Cartagena and go to the Visitor's Center. Just outside is a cab stand. You can have a driver AND guide at a very reasonable price and not be tied to a regimented tour.
The fort is your basic fort. Next, go to the Old City square and do some creative wandering. Your guide may accompany you or you can tell him to have a cup of coffee at one of the street cafes.
I did the wandering thing with a woman friend and felt absolutely no fear or anxiety.
Then, the Dungeons for shopping. As you face the shops, start at the left and work your way to the right. Tell your guide and driver to sit under a tree and wait for instructions. Duck into the first shop and buy them each a Coke.
They will be related to every vendor there and can be quite useful in the end game of negotiating. Practice shaking your head "no" and delivering a "shoo" gesture with your right hand to handle the street vendors.
No help here on Puerto Limon.
pamda -- CM First-Time Cruisers Editor