Zipaquirá is a city of some 70,000 people about an hour north of Bogotá, in Cundinamarca. It is Colombia's salt mining capital, and most famous for its Salt Cathedral, constructed almost entirely of salt within a now defunct mine.
Buses depart from Bogotá's Portal del Norte (on the Transmilenio line) for "Zipa" about every five to ten minutes, costing 3,500 pesos (roughly $2), making this a very easy day trip. On the way back, just walk down to Carratera 15 from the historical center, and buses will be leaving for Bogotá during daylight hours about every 30 minutes.
If arriving by bus, get off at Calle 4, which will take you up a pedestrian-only street past tons of shops and cafes to the main plaza in the historical center. After admiring the cathedral and overall very charming locale, turn left on Carratera 7 until you reach the end, then turn up the hill to see the Archaeological Museum. Through the large arch next to the museum is the path up the hill to the Parque de Sal, where you will find the Salt Cathedral entrance.