Visit nearby towns like Chia, La Calera, Cajica, Tabio, Zipaquira and La Vega. You can find cheap and fast transportation to any of this destinations either from the Terminal de transportes or the Transmilenio North Portal. From most, you can return the same day. But it's a good idea to get out, Bogotá is a chaotic city surrounded by lots of relaxed and peaceful places.
Choachà is the best kept secret in town. This small village 50 min. East of Bogotá is reached after climbing up and down a tall mountain, so tall you can see Monserrate at your feet. Local cooking, hot springs and a great Swiss restaurant await for you at your destination.