How do I create a climbable ladder?

I've been looking all over the place and on the internet, but I've not the faintest clue as how you can make a ladder than can be climbed by a standard FPS Controller. I tried looking at how VALVe does it for Half Life 2, but it's evil to try and emulate in Unity. I've no real skills when it comes to this part, so can anyone explain how to make a ladder that works in unity? Or does anyone have a prefab (That I can pay for in return)?

To make a ladder you need to tie it with your character controller script, but to give an example implementation with a controller script derived from the character animation demo. The ladder needs to have a collider set to trigger that's a bit larger than the ladder itself so player will trigger it when in close proximity to it. Attach the ladder script to the ladder and set bottom and top properties to the lowest and highest pos the player can reach, if you have difficulty to find the right values, uncomment the debug statement in the Move function.

The ladder script:

var bottom : float;
var top : float;

private var ctrl : CharacterController;

// function called by controller script to tell what it's character controller is
function WhoAmI(c : CharacterController) {
    ctrl = c;

// function called by controller script when controller is attached to ladder
// delta is the forward/backward movement
function Move(delta : float) {
    // we calc vertical position using current vertical position  + delta movement corrected for time interval
    var vertPos : float = ctrl.transform.position.y + delta * Time.deltaTime;
    ctrl.transform.rotation = transform.rotation;
    // Debug.Log("Move: " + vertPos); // debug usefull to determine top and bottom values
    if ((vertPos > top) || (vertPos < bottom)) {
    	// we're at top or bottom and moving away from ladder, use walk animation
    	ctrl.SendMessage("SetCurrentSpeed", delta, SendMessageOptions.DontRequireReceiver);

    	// set climb speed 0 to stop climb animation
    	ctrl.SendMessage("SetCurrentClimbSpeed", 0, SendMessageOptions.DontRequireReceiver);

    	// move forwards/backwards, orientation determined by lader orientation
    	ctrl.Move(transform.rotation * new Vector3(0.0, 0.0, delta) * Time.deltaTime);		
    else {
    	// no forward movement as we're climbing
    	ctrl.SendMessage("SetCurrentSpeed", 0, SendMessageOptions.DontRequireReceiver);

    	// set climb animation
    	ctrl.SendMessage("SetCurrentClimbSpeed", delta, SendMessageOptions.DontRequireReceiver);

    	var pos : Vector3 = transform.position; // get position of ladder, use it for x and z pos of the character
    	pos.y = vertPos; // the y pos (vertical) is determined by calculated vertical position
    	ctrl.transform.position = pos;

function OnTriggerEnter(other : Collider) {
    // tell controller we take over control
    other.gameObject.SendMessage("TakeOver", this.gameObject, SendMessageOptions.DontRequireReceiver);

function OnTriggerExit(other : Collider) {
    // tell controller we give back control
    other.gameObject.SendMessage("Release", this.gameObject, SendMessageOptions.DontRequireReceiver);

The adjusted Player Controller script:

var speed = 3.0;
var rotatationSpeed = 200.0;
private var curSpeed = 0.0;

private var vertSpeed = -10.0;

private var takeOverCtrl : GameObject;

// called when the ladder (or whatever wants to take control takes over the player)
function TakeOver(t : GameObject) {
    takeOverCtrl = t;

// we left the ladder (or whatever)
function Release() {
    takeOverCtrl = null;

function Update () {
    var controller : CharacterController = GetComponent (CharacterController);

    // Rotate around y-axis
    var newRotation = Input.GetAxis("Horizontal") * rotatationSpeed;
    transform.Rotate(0, newRotation * Time.deltaTime, 0);

    // Calculate speed
    var newSpeed = Input.GetAxis("Vertical") * speed;
    if (Input.GetKey("left shift"))
    	newSpeed *= 1.5;

    // Move the controller
    var forward = transform.TransformDirection(Vector3.forward);

    if ((controller.isGrounded) && (Input.GetKey("space"))) vertSpeed = 5.0;

    if (takeOverCtrl) {
    	// we have some object (ladder) taken over control 
    	SendMessage("SetCurrentSpeed", 0, SendMessageOptions.DontRequireReceiver);
    	// a bit of a hack to send two messages as the receiver can have only one parameter
    	// a better solution would to have the two parameters encapsulated in a object/struct
    	takeOverCtrl.SendMessage("WhoAmI", controller, SendMessageOptions.DontRequireReceiver);
    	takeOverCtrl.SendMessage("Move", newSpeed, SendMessageOptions.DontRequireReceiver);
    else {
    	// the normal movement handling
    	var delta = Time.deltaTime;

    	controller.Move((forward * newSpeed + Vector3(0, vertSpeed, 0)) * delta);
    	if (vertSpeed > -10.0) vertSpeed -= delta * 10;

    	// Update the speed in the Animation script
    	SendMessage("SetCurrentSpeed", newSpeed, SendMessageOptions.DontRequireReceiver);
    	SendMessage("SetCurrentLean", Input.GetAxis("Horizontal"), SendMessageOptions.DontRequireReceiver);

@script RequireComponent (CharacterController)

The ladder and player controller script also assumes there are scripts for handling animations, the `ComplexWalkBlend.js` from the demo project already implement the `SetCurrentSpeed` and `SetCurrentLean` functions but you must add an function `SetCurrentClimbSpeed` to have the char have a working climb ladder animation.

The ladder is not perfect, when at the top you need to climb down backwards, when walking forwards to the ladder you will move off immediately (as you holding controls forwards which is climbing up).

If you need more help, let me know.