JoAnn as far as i know there are no ruins in Jamacia. Lots of things you can do in Jamacia in a day. Have you done Dunns River Falls? also the river raft tour is a nice relaxing day, you are on long bamboo rafts and your guide gently polls the raft down the river, very scenic. Jamaica is one island where i would recommed booking a shore excursion through the cruise ship or hiring a bonded-cruise recommended driver for the day.
The 4 x 4 jeep excursion will give you the opportunity to take good pictures.
The only other place I would recommend in M Bay is Jimmy Buffet's Margaritaville, has a slide into the water, and trampolines out in the water to bounce around on. Was a fun place to visit. Don't take the highlights tour, it was awful, he drove so fast to just get us downtown to shop (not my cup of tea in Jamaica).
Interested in birds? See the Rocklands Bird Sanctuary located above Montego Bay. Gets spendy as the place is really a small private home back in the hills so the taxi has to wait for you, but how many times in your life can you feed a hummingbird while it sits on you finger?