Interesting idea. For decorative lighting, I can see using something similiar.Our tower does not however, have a catwalk, in the classic sense.
The tower looks very much like this one.http://content.answers.com/main/con.../24/150px-Carmel-indiana-water-tower.jpg
Access is through the middle, up a LONG ladder, and then with a small "crows nest" at the very top. Only about 8 feet in diameter, for the antennas. At the top, it's about 50' out to the edge of the structure, completely untethered.
There is limited power in the "shaft", just enough for lighting the inside well with the ladders.
It aint an easy one.