Leaving Costa Rica after New Years looking for a quick stop in Colombia. Safe for a solo female traveler. Cartegena? Or another suggestion?
It all depends on what you would like to do in Colombia. It also depends on the type of traveler you are.
If you are foodie and love art culture then you would love Bogota. It is filled with SOO many museums including my favorite Museo Botero. There are many foodie sections in Bogota including Usaquén Plaza area (an older colonial area of Bogota), La Macarena, Zona G or Calle 85 and other foodie places near Andino Shopping Mall. The drawback of Bogota is that it may require 3 days of acclamation if you aren't healthy and young. First time there I did not get altitude sickness but I get it now when I go back to visit.
Medellin is a very popular location. It is filled with gringos (I have a lot of American friends who live there.) It is also a very foodie and art friendly location. El Poblado area of Medellin has a lot of great places to eat and the region is very tourist friendly. Parque de los Deseos is nice to visit because of the science museum there and across the way is the Botanical Garden. There are SOOO many amazing parks in Medellin.
If you are looking for a more laid back environment you would enjoy Cartagena or anywhere on the coast. Cartagena is nice, but it is like Las Vegas of the USA. It does not represent what Colombia really is. Other great beach and laid back alternatives is Santa Marta, which has a lot of the same feel of Cartagena but with a lower costs and a bit more Colombian culture. A day trip to Taganga to enjoy the party/beach town would be worth it just to enjoy the sun. Tayrona National Natural Park is also near by if you want to plan your trip around that place instead. It is one of the most beautiful places in the world. I would admit has been very tourist ridden though in the recent years.
If you like coffee check out Eje Cafetero region. I love visiting this region every year. Fly into Pereira and use it or Armenia as a hub to visit the coffee region. Check out the beautiful small village of Salento to just relax and enjoy small cafes and small pueblo life. Or you can stay at the many fincas in the area and enjoy the silence of beautiful mountains and green hills.
Solo travels as a female you should be relatively safe. If you have blonde hair and blue eyes and light skin you will stick out like sore thumb so I would suggest staying away from downtown areas of Bogota. Otherwise the people of Colombia are some of the nicest people in the world. There is a reason I moved to Colombia.
Mentioned in this answer:
Cartagena is Colombia's most popular destination and easy to get to from Costa Rica. There's plenty of culture and history, and it's also got great food and night life.
If you want a break from the tropics, Medellín is vastly underrated. It's about 4500 feet above sea level so the climate is warm but not hot, and it's one of the safest cities in Colombia now that the drug cartels have moved away. It's somewhat off the tourist path and therefore a great place to experience Colombia rather than just see it.
Bogota is also a great city, but I wouldn't recommend it for a 3-day visit because it'll take your body that long to fully adjust to the 9000 foot altitude.
As for safety for a solo woman traveller, the same precautions apply to Colombia as anywhere else in the world: try to make friends with other women so you can work as a group, keep an eye on your drink at all times, don't drink to excess or do any judgment impairing drugs, and if you feel threatened by anyone don't be afraid to speak up and assert yourself.