Answer by Ashkan_gc

add a collider to that cube object that you want to change level when colliding with it. check the is trigger of the collider that you attached and write something like this in a script.

function OnTriggerEnter (other : Collider)
{
if (other.tag = "player")
{
   Application.LoadLevel ("levelname"); 
}

put the level name in the "" you can expose this as a string and set it inside the inspector or just create a manager.