void CanIClimbThis () {

float testDistance = 20;

RaycastHit[] bumperHits;

Vector3 newForward = transform.forward;

bumperHits = Physics.RaycastAll (

transform.position,

transform.forward,

testDistance);

Debug.DrawRay(

transform.position,

transform.forward * testDistance,

Color.blue

);

if (bumperHits.Length>0) {

Debug.DrawRay(

bumperHits[0].point,

bumperHits[0].normal,

Color.red

);

// to find the left/right angle of the

// obstacle ahead of you, use this.

// Determine the cross vector for the point.

// We're interested in

// the y axis spin, so use that.

Vector3 crossAxis= -Vector3.Cross(

transform.right,

bumperHits[0].normal);

// Determine the angle at that point.

float angleAtWall = Vector3.Angle(

transform.forward,

crossAxis);

print("angle is" + angleAtWall);

if (angleAtWall>135) {

print("I can go up this");

} else {

print("I should probably go around");

}

}

}

void WhichWayToTurn () {

float testDistance = 20;

RaycastHit[] bumperHits;

Vector3 newForward = transform.forward;

bumperHits = Physics.RaycastAll (

transform.position,

transform.forward,

testDistance);

Debug.DrawRay(

transform.position,

transform.forward * testDistance,

Color.blue

);

if (bumperHits.Length>0) {

Debug.DrawRay(

bumperHits[0].point,

bumperHits[0].normal,

Color.red

);

// to find the left/right angle of the

// obstacle ahead of you, use this.

// Determine the cross vector for the point.

// We're interested in

// the y axis spin, so use that.

Vector3 crossAxis= -Vector3.Cross(

transform.up,

bumperHits[0].normal);

// Determine the angle at that point.

float angleAtWall = Vector3.Angle(

transform.forward,

crossAxis);

print("angle is" + angleAtWall);

if (angleAtWall<90) {

print("I should probably turn right");

} else {

print("I should probably turn left");

}

}

void showCollisionNormal () {

float testDistance = 20;

RaycastHit[] bumperHits;

Vector3 newForward = transform.forward;

bumperHits = Physics.RaycastAll (

transform.position,

transform.forward,

testDistance);

Debug.DrawRay(

transform.position,

transform.forward * testDistance,

Color.blue

);

if (bumperHits.Length>0) {

Debug.DrawRay(

bumperHits[0].point,

bumperHits[0].normal,

Color.red

);

}

}

Find the normal of the collider in front of you, based on a ray cast.

Here's how (in Unity3d)