I've been to Superman's Fortress of Solitude and it's inside a hill in the small town of Zippaquira just north of Bogotá:
If you're a bit rusty on your Superman references, the Fortress of Solitude was Superman's vacation home. He'd go there to rest, reflect, and get his strength back. Unfortunately, I've lied and the Fortress of Solitude isn't in Zippaquira but what is there is just as cool. Inside this mountain is a Halite (rock salt) mine that they created a church in, thus the name Catedral De Sal:
The mine has been in use for almost seven thousand years (!!!) and continues to be worked today. Miners first built a chapel in the 1930s as a place to pray for protection while they worked. Over the years, the church was made bigger and was in use until 1990 when it had to be closed due to structural issues. The new church was started in 1991 and is located about 200 feet deeper than the original. To get to it, you enter through the door in the photo above and walk down a mine shaft that's about 10 feet tall. Note the salt leeching through the rock:
As you walk down, down, down to the main church, you pass 14 small chapels along the way. Each stop is a station of the cross. (By the way, it's not as dark and claustro as the photos make it look.)
Like I mentioned, the mine is in active use. There are parts of the mine that are accessible, especially when you visit the restrooms, that are "unfinished". This is what the mine looks like when they're done removing the rock and salt from an area:
What they've done, very well I might add, is to take the previously-excavated areas of a working mine and transform them into a series of amazing spaces. Your first view of one of the main parts of the church is what's below. The scale of what you're looking at is not clear from the photo. My guess is that this particular room is 60 feet wide and 120 feet tall. I can't even estimate how far away that cross is. Those black squares on the ground are rows of pews. Also, note the cool "marbling" texture on the ceiling.
The space is impressive. The salt and rock textures on the walls and ceilings are highlighted with various colors of lights and the whole experience is a bit like what Superman's Man Cave could have been if it weren't white crystal.
I think this photo of two of the four large columns that have been cut out of the rock along with the people and pews helps to give you some idea of the scale. My guess is that the columns are 15 to 20 feet in diameter.
Here's a photo that shows the salt-and-rock texture of the ceilings and walls. You can also see a "waterfall of salt" effect (where the pink lighting is) on the front wall of this part of the church.
After taking the tour, and probably just like when you're hanging out at Superman's fortress, you can grab a drink while you're here. Yep. This church has a cafe inside!
The Catedral De Sal is very well done. To see the architectural design alone is worth a visit. It's probably the most spectacular "building" that I've seen in Colombia and definitely the most unique church.