AFAIK in regular C a T[][][] foo would be a the same as T ** foo, so it gets implemented as a pointer to an array of pointers to arrays of pointers, each pointing to contiguous allocations of multiple Ts, each not necessarily near the other. So you need three dereferences to get to an element.

  T value = foo[1][2][3];  // becomes:
  foo ->  (T **)
          (T **) -> (T *)
          (T **)    (T *)
          ...       (T *) -> (T)
                    (T *)    (T)
                    ...      (T)
                             (T) <-- This one!

This allows for jagged arrays, yay! So useful.

This is in stark contrast to a Fortran-style array, which is allocated as one contiguous piece, all dimensions folded up for linear access with one dereference.