I'm from Barcelona, Spain, but I've been to Colombia some years ago for a project for an important spanish bank. I was there 5 times, and the total stay where 8 months. You should travel around the country, but while you should definitively visit Bogota, keep in mind that this city is in the middle of the Andes, and it is 2.600 meters above the sea level. That means that the weather can be colder than on the coast (nothing really cold, but more rainy sometimes) and the temperatures can be 15º-25ºC, while on the seaside the temperatures are more like 30º-40º. It is in the tropic, so there are no 4 seasons, just the wet season and the dry season.
You should go to San Andres Island, Santa Marta, Cartagena, Cali... it's a must to do scuba diving on all these places, don't miss Tayrona National Park!! I also enjoyed my trip to Leticia, in the middle of the Amazon Jungle, just where Colombia frontiers with Brazil and Peru.
Enjoy and take care!!