10 day itinerary in Colombia- No idea what to make of it.

I am planning a trip to Colombia next week. I'll have 10 days/9 nights to spend there, arriving via flight in Bogota at 2230 the first night.
Cartagena is #1 on my list right now, so that is a must. Mind you, I do not speak Spanish and will be there on my own.

Don't want to rush things to much, and don't want to spend a lot of time in transit, so with that being said, I want to do Bogota for the first 2 nights maybe, since I'll already be there. From there I was thinking I'd fly to Cartagena and spend 4 nights there. This leaves me three nights to spend in any other city. I work for an airline, so my flight USA-Colombia will be free. We have agreements with LAN, COPA, and Avianca that will allow me to get a ticket for around $30 for any domestic flights, so somewhere with a flight out of Cartagena would be nice.
Any suggestions? Won't lie, I like a good party scene, and a city where I can just walk around and explore and discover things.