Wow, it looks impressive from that angle.
This is a simple idea done with some modern materials to give it an interesting look. Just a magnet on a string, held up by a pair of very strong supermagnets.
I made the structure out of clear acrylic. It's a great material to work with, as you can weld two pieces together with a solvent and create a seamless bond. I get mine from a local Tap Plastics store which sells scraps which are perfect for the odd creation.
A few more pictures from my porch. Depending on how much string you let out, the magnet will hang loosely or pull strongly upwards. I added some clear rubbery padding underneath to help when the magnet slips and slams upward but it's still quite an impact.
The magnet itself has a hole in the center and the fishing line is tied to a metal post with an endcap to keep it secure. Trying to tie a string around a magnet would require weaving a sock to keep it from slipping between the threads.
Given the right adjustment, it will sqing in a pendulum arc for quite a while before air and rope friction bring it to a stop. A fun desk toy, as long as you keep it away from your other magnetic desk toys. I DO have that problem...
Here is a closeup of the adjustment for the sting. Just a simple butterfly screw to clamp down on the string that runs through the acrylic. Acrylic can be drilled if you go easy and use cell cast, not extruded. Even extruded will work, you just have to have paitence and practice.