Hi Sue!
Didn't realize you were going to have a stop in Guatemala...and sorry I just got to this thread.
It's actually Santo Tomas de Castilla, it is on our Caribbean side. You have a few turisty options available (Rio Dulce and the garifuna town of Livingston) closeby and of course, depending how long you are in port, possibly a visit to Quirigua or even Tikal. If coming in by cruise ship I would recommend booking thru the shore excursion OR use this travel agency in Guatemala:
Clark Tours . They are the most trusted outfit back home (my parents use them to book their Europe trips) and have been around like forever...they are not a fly by night operation. They may be able to set something up (depending on what you want to do) and meet you at the port.
The port really won't have anything to do, they have a like a little market area but beyond that, nothing of note...you would have to hitch a ride somewhere.
Hope this helps!