The Salt Cathedral is one of the must-see sights around Bogotá. It is an enormous cathedral built out of a salt mine, complete with a baptismal font, the twelve stations of the cross carved in salt rock, and enormous stone statues bathed in a weird blue light.
It's fairly easy to get to the Cathedral. You can take a bus from Bogotá's main terminal, or you can take the Transmilenio to the Portal del Norte (lines 50, 60, 70, 100, 25) and transfer to a feeder bus from there. I would recommend the Transmilenio, especially if you're staying in the centro, since it is faster and cheaper. The route is about 1-1.5 hours.
Another way is on the "Tren de la Sabana" (Savannah Train), which leaves on weekends and holidays at 8:30am from the "Estación de la sabana" in the Zona Norte. The fare is 21,000 pesos for adults and 14,000 for children. I missed the train, so I can't comment on it. If you do take it, be sure to go on a Sunday so you can see the Mass that takes place at 12PM.
Once in Zipaquirá, it was easy to find the Cathedral. We took a few pictures around the main square, which has a nice church, and made the hike up to the mine. We found it pretty exhausting, considering that we hadn't had much time to adjust to the altitude. There is no bus service. You can take a taxi, but the path up to the Cathedral is worth seeing.
Upon reaching the top, you can walk around the park and take in the view of Zipaquirá, which is nice. Tickets to the Cathedral cost 10,000 pesos for adults and include a guided tour, which starts every half-hour or so, and is available in various languages.
The Cathedral is an impressive work, and really a monument to the ability to use heavy machinery. There are huge sculptures that took months to be crafted out of salt rock, and I suppose an observant Catholic will find the stations of the cross inspiring. I thought they were particularly creative, since the sculptors had to figure out how to represent Jesus's movements without actually showing Jesus. The tour guide explained how each station related to the sculpture used to present it. The Cathedral also makes use of a variety of optical illusions, but I won't give them away.
In all, a beautiful work of art that surpasses many classical buildings in sheer creativity. I would have liked to take the train and see the Mass, but I'll have to reserve that for my next visit.