I've been traveling to Colombia at least every 3 - 4 months for the last 5 years... It's an awesome country..... Don't let anyone scare you about the drugs and rebels (people who tell you that are people who have never been to Colombia)... Colombia is like any country you travel to... you need to take the same measures to ensure your safety as you do in Mexico or even Ecuador (I've traveled extensively to them as well).
Anyhow, to answer your question on places to see. Since I'm not sure where you will be I'll list my favorite places/cities in order:
- Medellin: This is my favorite city because it's beautiful as well as fun. They have a metro, pueblito paisa, outside the city you can go to the piedra del penol (worlds largest rock. it has an amazing view), and there is plenty to do with the night life and good eateries.
- Bogota: The capital city is beautiful. The museum de oro, the historic colonial district and you should venture out on a tour to the Cathedral of Salt it is definately not to miss (on your way back stop and eat at Andres Carne De Res. It is some of the best steaks you will find). Also you can see the capital from Mt Serrat.
- Cartagena: This place is awesome if you like colonial architecture. The beaches are ok for hanging out becareful in the water as the undertow is rough. Your best bet is to take a tour to the islands of rosario (Islas de Rosario)... the tours usually include a visit to the acuarium and a private island or the island of Baru.... the waters at the islands are carribean blue and awesome for snorkeling.
- Cali: Cali is always fun but it's gotten a bit rough over the last few years.
B) What to do to prepare for your vacation.
- Since you don't say where you're planning to go you should pack for all weather. Couple pairs of jeans, shorts, sandals, walking shoes, light jacket and shirts. Bogota can be cold at night, but the climate is similiar to Los Angeles. Medellin is warmer than Bogota and Cartagena and Cali are hot and humid.
C) Food is great wherever you go. Colombian food is mainly meat and potatos so you probably won't have any issue's.... but be adventurous and try everything.
Music is awesome and it's tropical - Merengue, Salsa, Vallenato, Cumbia, etc. Have fun.
Festivals - remember that 7/20 is independence day.
I love Colombia... the people are great and friendly, the food is fantastic, the culture is marvelous..... I love it so much I married a Colombian woman. ;)
Don't let anyone scare you... Colombia is safe as long as you use your common sense and are aware of your surroundings. That's the same advice I give to anyone traveling to any country that is not the USA.
PS. Feel free to email me if you want to chat further.