Here is a little dumper I wrote some time ago:

my %h2 = (
    'AAA' => 'aaa',
    'BBB' => 'bbb',
    'CCC' => {
        'A1' => 'a1',
        'B1' => 'b1',
        'C1' => {
            'A2' => 'a2',
            'B2' => 'b2',
            'C2' => 'c2END',
        },
    },
    'DDD' => 'ddd',
);

sub ddump
{
    my $ref = shift;
    my $deep = shift||1;
    for my $k ( sort keys %$ref )
    {
        if ( ref $ref->{$k} )
        {
            print "\t" x $deep."$k =>\n";
            ddump( $ref->{$k}, $deep+1 );
        }
        else
        {
            print "\t" x ($deep)."$k => $ref->{$k}\n";
        }
    }
}

ddump( \%h2 );
[download]

Then I found a column by merlyn, which gave me the idea of dumping into a CGI table structure. The result:

use CGI qw /:all -nph/; #on Win32
$|++;

    sub nest
    {
        my $it = shift;
        ref $it ? complex_table($it) : $it
    }

sub complex_table
{
    my $hr = shift;
    # could test here to ensure that $hr is indeed a hash ref.
    table( { -border => 2, -bordercolor => 'green', -cellspacing => '0
+', },
        map Tr( td( {-valign=>'top'}, $_ ), td( nest( $hr->{$_} ))), s
+ort keys %$hr
    );
}

my %h1 = (); # feed your HoH here

print
    start_html,
    complex_table( \%h1 ),
    end_html;
[download]

which produces a dump like this:

AAA	aaa
BBB	bbb
CCC	A1 a1 B1 b1 C1 A2 a2 B2 b2 C2 c2END
DDD	ddd