We took the Panama Canal railroad offered by Carnival. For us, we really enjoyed it! We took a bus for about 20 minutes and got to see Colon. True, Colon is poor and dirty, but a lot of Central America is poor and dirty. We got the railroad and we had an interesting tour guide. His name was Uncle Marty. He was a little creepy, but generally, he did a great job along with all of his staff. We learned a lot about Panama and the Canal. Panama is really nice I think - but the country wouldn't be so nice if it wasn't for the Americans being there during war time and setting up all the infra-structure. We took the train for about an hour and saw the boats right by the canal. It was very nice. When the train ended we got on the bus and went to the Mira Flores locks. We didn't get to see any boats go through the canal, but it was really cool to see how everything worked. We were there in December, and it was very hot. About 95 degrees. We then got back on the bus and went to the Pacific Ocean and saw beautiful Panama City. We didn't get to go in the city, but saw the view. It looked very nice and somewhere I would like to go again.
On the way back we were supposed to take the bus back to the Colon, but we lucked out and got to take the train back to Colon. They provided a nice boxed lunch and sandwich. They sang on the train, and had snacks. In all, we would recommend this very nice shore excursion and going to Panama is really nice.
I myself wouldn't going into Colon, but met a couple who said they went into Colon and had a nice time.