Very interesting history of these two countries - indigenous people, the Spanish conquest (always amazing that they traversed around the bottom of South America to settle/conquer the west coast of South America), liberation, modernization and population increase - recent high crime now under pretty good control in Colombia. It looks like the indigenous people are treated pretty well these days.
We flew to Cartagena via Panama City where we had a canal tour. Glad we had the opportunity to see that. Building that had such a huge effect on the world; and they have recently expanded it to accomodate larger ships.
Cartagena's walled city is really neat; it was hot and humid but still really nice walking around looking at people, houses, and street scenes. A good way to start the trip.
Then we went to Bogota. The altitude (8,662 ft) kept the weather cool. Bogota is a huge city - really nice museums, not as pretty - very impressive bus transportation system. And we definitely felt the altitude. Spectacular churches in all the cities we visited.
Then we went to Quito. From Quito we took a short trip to Otavalo, the site of a huge market. I really liked walking around the streets of the old town of Quito - it is surrounded by slightly higher mountains with houses on the hillside. so lots of scenic views. There were a couple of side trips up hills that we could have taken, but the weather wasn't quite clear enough to merit doing it.
Then we took the four day Tren Crucero trip from Quito to Guayquil. It was a nice refubished train - with very nice and well-informed guides (English and Spanish speaking) and we made various tourist stops. We were at the end of the rainy season and this part of the trip had clear skies most of the time. Saw lots of high mountains and volcanoes on the way. A highlight was the visit to the Rose factory/plantation. There were various forms of entertainment with visitors on the train. I highly recommend it.
Rail South America runs various other trips - some are one day and then there is the three week Buenos Aires trip to Peru including Machu Picchu. And I've been tempted by the Lima to Huancayo trip where I read once that conductors carry oxygen in case you need it because of the highest point which is 15,686 feet.
Then a day in Guayaquil including walking around an old section on a hill - nice small church of course and a pirate ship. We did spend a bit of time in Guayaquil in 2010 on the way to and from the Galapagos.
We stayed in several small boutique hotels that were quite nice: Casa Pombo in Cartagena, Casa El Éden in Quito, and two nice Hosterias on the train trip: Hosteria La Andaluza in Riobamba and Hosteria D'Franco in Bucay.
I recommend this trip and note that wasn't my first time: 51 years ago I went to these cities and took the then one-day train trip from Guayaquil to Quito. It was not a tourist train - at one point a woman got on carrying a bag of chickens (live). It is interesting to note that the population of Bogota then was under 1 million; now it is about 8 million.