as already stated earlier by johncena1, those places are 'disabeled because there is no collision, so you'll fall into the void.
use injector:
bindKey ("I","v = game.game:GetActivePlayer():GetPos() v.y = v.y + 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("J","v = game.game:GetActivePlayer():GetPos() v.x = v.x - 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("K","v = game.game:GetActivePlayer():GetPos() v.y = v.y - 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("L","v = game.game:GetActivePlayer():GetPos() v.x = v.x + 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("U","v = game.game:GetActivePlayer():GetPos() v.z = v.z + 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("O","v = game.game:GetActivePlayer():GetPos() v.z = v.z - 2 game.game:GetActivePlayer():SetPos(v)")
and move yourself (on foot) through the invisible walls using I J K L for north east west south and U O for up down.
use injector:
bindKey ("I","v = game.game:GetActivePlayer():GetPos() v.y = v.y + 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("J","v = game.game:GetActivePlayer():GetPos() v.x = v.x - 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("K","v = game.game:GetActivePlayer():GetPos() v.y = v.y - 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("L","v = game.game:GetActivePlayer():GetPos() v.x = v.x + 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("U","v = game.game:GetActivePlayer():GetPos() v.z = v.z + 2 game.game:GetActivePlayer():SetPos(v)")
bindKey ("O","v = game.game:GetActivePlayer():GetPos() v.z = v.z - 2 game.game:GetActivePlayer():SetPos(v)")
and move yourself (on foot) through the invisible walls using I J K L for north east west south and U O for up down.