Actually, I just learned the answer a few weeks ago when I toured a wind-farm: Vestas uses magnets to secure ladders, lights, and other items to the inside of the tower instead of drilling holes. This neatly heads off problems with water egress and rust.

It is a little daunting to see that ladder going up into the dizzying heights and see that it is held in place by the same technology that keeps the kids' art stuck on the fridge.

Here's their patent on it: https://www.google.com/patents/US8567131