International flights from both Europe and the US fly directly to Bogota and both airports, El Dorado and Puento Aereo, are served by busetas and colectivos which have Aeropuerto clearly marked on the front. You will find these on Calle 19 or Carrera 10 for your return journey. You can also take a taxi which will cost you about US$6.
Colombia has road connections with Venezuela and Ecuador but some of the border crossings come under regular guerilla attacks and it is not recommended to enter the country using such crossings. You can also enter the country by boat but Bogota is quite a distance from the major ports and again the journey can be quite an ordeal.
While most of the main tourist attractions are within walking distance of each other, it is always helpful to know that the bus service in Bogota covers the entire city. If you are feeling a little drained, all you usually need to do is put your hand out when you see an oncoming bus. There are some official stops but these are not that common and are mainly located on Carrera 7. The very reasonable fare is always written on the door or the window.
If you are getting a taxi, insist that the driver uses the metre. There is a standard charge of about US$1.25 before your journey starts and after that the fare is calculated by units which are transferred into pesos. There should be a chart in every taxi showing you the list of units so you can ensure that you are not being overcharged.