The Great Zipper Climb of Guatapé
Another fun little city for a day trip outside of Medellin is Guatapé where you can climb the 649 zipper-like steps that are wedged between a crack that runs the length of the 385 meter tall El Peñón. The modern day steps are made of concrete and bricks, but the maze-like stairway that intertwines upon itself several times like a strand of DNA is said to be based on the original set of sticks that were wedged in place to allow the first climber (and then owner of the property) to reach the top.
Oh, and speaking of climbing to the top. Make sure you check out the very last photo at full size for a pretty incredible shot.
