We didn't book an excursion through the ship. You might want to. We ended up getting a cab for $45 plus tip for three hours, which included a driver and a tour guide. It worked out well because we got a good guide, but he had to take us to the emerald shops he gets kickbacks from. We had no intention of buying anything in those shops and didn't. This was by far the worst port I've ever been in when it comes to locals pushing their wares. Every 10 feet someone was putting hats on our heads, jewelry on our wrists or t-shirts in our faces. I get it, that's how they make money and survive, but it gets really, really frustrating very quickly.
The old walled city is lovely despite the peddlers. We went to the Inquisition Palace, which was cool but small. It also includes a Cartagena history museum. Our driver also took us to the new city, which he called Second Miami. It's not something anyone really needs to see and we ended up at an emerald "museum," which was nothing but a big store where you see the emerald workshop.
We liked the Fortress and the old town and got lots of great pictures, but didn't really feel comfortable in this port. But hey, at least we can say we went to Colombia :)
Aruba is beautiful. Period. We hopped on a Fofoti Tours bus for $20/pp that was to take us to the Casibari Rock Formations, an old church (the name of which escapes me), and the California Lighthouse, then drop us off at Palm Beach for two hours, pick us up and take us back to the port. Everything was great until the tour bus never came back to pick us up. The two of us and one solo passenger got off the bus at 4:20 and agreed to meet the driver back at that spot at 6:20. All three of us got back to the meeting point at 6:05 and waited until 6:45. No bus. We were able to hop on one of the DePalm shuttles that happened to be running from one of the casinos past the port to the airport and make it back on board before our 7:30 all-aboard time. Other than the terrible service we received from Fofoti Tours, Aruba was wonderful.
We didn't explore the island, just walked around on either side of the bridge. We liked it, though, even though we didn't do much shopping (that's not why we go on vacation). There was plenty to see within walking distance of the port, including an old fort that has been converted into an outdoor shopping mall. And there's a KFC and a Pizza Hut, if you're hungry :)
We grabbed a cab to Maho Beach, specifically the Sunset Beach Bar, to watch the planes come in and take off for a few hours. It was a lot of fun, but very busy. We didn't eat there; some friends recommended a place called Lee's, so we got a cab to take us there and weren't disappointed. It's right on the main road and any cab driver will know it. They have some of the best BBQ chicken I've ever tasted and the fried plantains are amazing, not to mention the homemade BBQ sauce on the tables.
When I was in St. Maarten in 2012, I went on the Golden Eagle sailing catamaran, which took us to Mullet Bay for snorkeling and beach time. That was also a good experience and the crew on the Golden Eagle was great. That trip included drinks, sandwiches and snorkeling equipment. They are also somewhat famous for their YMCA dancing at the end of the excursion.
We took a cab to Red Hook and hopped on the ferry to St. John. The information given to us when we got off of the ship listed the prices incorrectly, so what we thought would be a $10 cab ride was actually $20. It was worth it, though, because St. John is absolutely beautiful (the Charlotte-Amalie ferry doesn't run often enough, so you pretty much have to go to Red Hook where it runs every hour). We went to Caneel Bay and used the beach there. It was sheltered, calm, quiet and the water was crystal clear. We also found a nice little hiking trail about five minutes away from Cruz Bay where the ferry lets out and spent a half hour or so hiking before heading back to the ferry terminal. After getting back to Havensight, where our ship was docked, we did some souvenir shopping and had drinks and tacos at what I think was called the Dog House Saloon. Both the beer and the tacos were fantastic.