Ascending single or double ropes is most often practiced in rope access, tree climbing, caving or technical climbing. Ascending a single rope will often involve a Jumar [1] and a camming device placed on your foot or chest. Ascending a doubled rope can be done with just the rope using Blake's hitch or some extra material and a Prusik knot.

[1]: http://en.wikipedia.org/wiki/Ascender_(climbing)

Such imagined one-way leg powered rope sliders exist[1]! They work well, but surely would be tiring and—after exiting a jacuzzi into a windy void—I'd have to imagine quite cold.

1. http://en.m.wikipedia.org/wiki/Ascender_%28climbing%29

You don't actually need the hardware -very similar results can be achieved using a spare piece of rope and a prussic knot*.

((I really hope I got the knot name right.))

Prusik knots are difficult to push up a rope, but there is a simple improvement you can do using a carabiner: https://www.google.com/search?&q=bachmann+hitch&tbm=isch

That's extremely pleasing -thank you :)

Certainly! (And you have the knot right). It would likely be a bit more tiring/challenging for beginners though.

True, but using actual ascenders is so much quicker and easier than doing it with prusik knots.

Very true -I guess the point I was trying to make is that if you find yourself at the bottom of a rope _without_ an ascender to hand, all hope is not lost. (though admittedly, I'd probably need a working internet connection to be able to remember how to tie a prussic ;) )