My cats are approaching nine years old, but when they were kittens, the shorthair was quite the acrobat. One day I walked into the living room and found her just as happy as a clam atop a 7' bookcase. Several times over the next couple weeks, I'd come home to find her sleeping there, but could never figure out how she made it. Then one night she decided to make her ascent while I was watching TV -- she just lept straight at the side of the bookcase, made it to about the halfway point, and climbed right up the side until she reached the top.
Had I looked for the tiny little claw marks in the oak, it probably wouldn't have taken me quite so long to figure out how she was getting up there.