bel·fry
 /ˈbɛlfri/  noun  ,  pl   -fries [  count  ]
  : a tower or part of a tower where a bell or set of bells hangs
  bats in the/your belfry
    informal + old-fashioned  
   ◇ To have bats in the belfry or (chiefly US) bats in your belfry is to be crazy.
    an old woman with bats in her belfry [=a crazy/batty old woman]