We used a mining technique called raise boring. Take a look at the video -- it's an interesting operation. Instead of drilling down from the top, you pull a large diameter reamer up to the surface from the bottom using a smaller diameter pilot hole -- more efficient than a top-down drill because the rubble isn't fighting gravity. It rains down beneath the advancing bore and gets hauled out a horizontal shaft at the bottom. Our next major step will be cutting the spiral stairway using a robotic stone cutting saw. In parallel, we're also manufacturing and testing the Clock components.
For the impatient, awesome parts are at 0:23, 1:20, 2:05, and 3:15 (that last of which reminds me of the DNA Lounge "See Snake" video.)