Colombia is an enormous country, meaning it will take you a lot of time travelling from A to B. The best way to do this is travelling by bus. There are a lot of different bus companies, in my personal opinion, Expreso Bolivariano is the best of all. Book your bus easily through www.busbud.com

Another way to travel the country is by plane. Plane tickets can be cheap if you don’t buy them last minute. VivaColombia is the cheapest airline, but beware of the luggage weight. I’ve heard many bad stories about this airline. I used it twice and everything was just fine. I’m not sure if I was just lucky they didn’t charge me extra for my luggage. Latam is the other big airline in Colombia and South America but is a little bit more expensive. 

When you take a taxi in Colombia, always first tell your destination and ask a price, then negotiate before you get in the car. Taking a taxi is very safe, just don’t overpay. 

When you need cash, try to find the bank Pichincha. At this bank you can withdraw a high amount of money without an extra fee. You will save a lot of money this way. 

If you want to buy a local sim card, buy one of the network Claro. It is cheap and has the best coverage in the country. Don’t buy a sim card on the street but go to a real phone store. 

For a two week travel in Colombia, arriving in Bogotá, I would recommend following this schedule. 

Day 1 Arriving in Bogotá
Day 2 (Night) bus to Salento (9 hours)
Day 3 Salento 
Day 4 Bus to Medellín (4 hours)
Day 5 Medellín
Day 6 Medellín
Day 7 Flight to Cartagena (1 hour)
Day 8 Cartagena
Day 9 Cartagena
Day 10 Bus to Santa Marta (4 hours)
Day 11 Santa Marta, Tayrona park, Costeño beach
Day 12 Santa Marta, Tayrona park, Costeño beach
Day 13 Santa Marta, Tayrona park, Costeño beach
Day 14 Flight to Bogotá (1 hour) 

If you have three weeks, this is a realistic schedule. 

Day 1 Arriving in Bogotá
Day 2 Bogota
Day 3 Salento
Day 4 Salento
Day 5 (Night) Bus to Neiva (8 hours)
Day 6 Neiva 
Day 7 (Night) bus to Cali (9 hours)
Day 8 Cali 
Day 9 (Night) bus to Medellín (9 hours)
Day 10 Medellín
Day 11 Medellín
Day 12 Medellín
Day 13 Flight to Cartagena (1 hour)
Day 14 Cartagena
Day 15 Cartagena  
Day 16 Islas del Rosario
Day 17 Islas del Rosario
Day 18 Santa Marta, Tayrona park, Costeño beach
Day 19 Santa Marta, Tayrona park, Costeño beach
Day 20 Santa Marta, Tayrona park, Costeño beach
Day 21 Flight back to Bogotá