In Limon I went to the Sloth sanctuay cause I love animals, I was very disappointed I could not hold a sloth like seen in the photos. This maybe due to liabilty issues with Carnival. It was a short interesting excursion the Sloths were very cute, I don't reccomend eating the fruit they give you wonderful but made me sick (montezuma) If I go back I will go white water rafting my friends did it and loved it!
In Colon I did the Grand Tour with Carnival a nice combination tour.I didn't want to look at the canal all day so they take you to the Gatun lock to see a ship pass, then you get in a boat in the gatun lake (very pretty my favorite part) and go to meet the Umbria Indians who do a dance, and have a Q&A session with the chief, and can purchase hand made crafts. Buy your souveniers here they were the cheapest off all the ports and the money goes to the Indians to maintain their lifestyle.
I haven't been to Costa Maya yet but I will be. I think I will take a tour of the Mayan ruins there.