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In the show Game of Thrones there is this thing called The Wall. It is a monstrous, 300 mile long bulwark consisting of a fortified ice wall that is 700 feet high (check the wiki for more details). There are also castles/forts along the foot of this wall, as garrisons for the soldiers manning it.

Now, quite conveniently, at some of the castles there exists a sort of elevator built to reach the battlements from the castle 700 feet below the top of the wall. We can see the elevator is built from wood and metal and seems to be a fairly simple construction. No actual mechanism is shown. At the bottom is a lever, that when turned either sends the elevator cabin up or down respectively.

Given world like the one presented in Game of Thrones—What could be used to power the elevator?

Assumption:

• No magic


• The tech level is that of an (at most) late-medieval'ish civilisation


• Should work in the cold weather required to preserve an ice wall

Requirements:

• Works with as little work from people and or animals as needed.


• Can be operated by some sort of lever or switch (either at the top or bottom)


• Maintenance needs should be as low as feasible

Note: I'm aware there might be a canon answer in the books (though I don't remember anything too specific). That is not what I'm asking for, and this would be the wrong Stackexchange to do so anyway. I'm wondering for general reality-based solutions for this problem outside of the actual Game of Thrones context.

With counterweights it could be possible to have a "self-powered" elevator in these conditions.

The elevator must be counter-weighted by default with a mass that will make it slowly go down if activated (to activate it, it should be sufficient to manually remove some lock).

This will allow the elevator to go down empty.

if we instead want it to go up empty, we should attach a small additional counterweight, to reach a mass higher than the one of the cabin.

if we want to go down, with people or materials, we still need to attach more counterweight, to reach a balance and avoid a too fast descent.

If we want to go up, with people or materials, we need to attach a heavier counterweight, to surpass the cabin (and content) weight.

The problem is. these counterweights (except for the default one, which is always attached) will remain on the ground level once used and we should return them up to use them. Which will require human or animal work and defeats the purpose.

To solve this issue we could simply use blocks of ice/snow, that presumably self-generate at the top of the wall. In fact, imagine that the pathways on the top must be kept clean, and some excess of snow will be found every day.

So, let's say that there is a set amount of mass that can be lifted each day (varying day by day based on weather conditions?), but this could be an efficient solution.

Edit:

The lever could actionate a mechanism that attach the cabin to a heavy or light counterweight, inverting the direction of the elevator. However, manual work will still be needed after the travel to tare and reapply the weights

Good old pulleys

A major improvement from the 4th century BC and still in use today, is the compound pulley: a combination of single pulleys in a block. The mechanical advantage equals the amount of pulleys used.

A crane with a triple pulley (a "Trispastos") has two pulleys attached to the crane and a free pulley suspended from them. It offers a mechanical advantage of 3 to 1. A crane with five pulleys in a similar arrangement (dubbed a "Pentaspostos") offers a mechanical advantage of 5 to 1.

Using a compound pulley a man can lift more than he is otherwise able to. If a single man pulling a rope can exert a force of 50 kg, he can raise (or lower) 150 kg using a Trispastos and 250 kg using a Pentaspostos. The same goes for the rope. A rope with a tensile strength of 50 kilograms can be used to lift (or lower) 150 kilograms if 3 pulleys are used, and 250 kilograms if 5 pulleys are used.

And you can pull the rope using winches and capstans

Coming down is easy, you just need a braking system, so I won't worry too much about that. Going up is the hard bit.

1. Donkey power

Nice and simple, the horse powered pump or winch is a bit of technology as old as time. In this case you're going to use your donkey/ass/mule/horse to winch a weight up to the top of the wall. When you want to ascend the pulley with the weight is linked to the pulley with the lift. Weight comes down, lift goes up. The equine is then returned to duty winching the weight back up.

2. Water power

A similar system to the horse winch but this time the counter weight is a water tank refilled at the top and emptied when at the bottom. You pour enough water into the tank that the lift starts to rise, you can also use this as part of your braking system by removing only just enough water that the lift starts to fall. Appropriate speed controllers should remain in place.

3. Men in a hamster wheel

This is a very old system for controlling such systems, used in the appropriate period for cranes when building castles. This could also be the equines from method 1 controlling the winch directly.

The lever

Rings a bell to tell whoever is in control to do their job. Control systems aren't worth the hassle in the age of manual labour.