my %hash=('ID' => {
                  'key1' => [ "key1_val1", "key1_val2" ],
                  'key2' => [ "key2_val1", "key2_val2" ]
                  }
          );

foreach my $id (keys %hash ) {
    foreach my $keyno ( sort keys %{$hash{$id}} ) {
        for (my $keyvalno = 0; $keyvalno <= $#{$hash{$id}{$keyno}}; $keyvalno++) {
            print "$id - $keyno - $hash{$id}{$keyno}[$keyvalno]\n";
        }
    }
}