$dd{'1'}{'2'}{'3'}="hi";

##</code><code>##

my %dd = (
    1 => {
        2 => {
            3 => 'hi'
            }
        }
);

##</code><code>##

my $hash_ref1 = $dd{1};
print $hash_ref->{2}{3}, "\n";
# prints h1

##</code><code>##

while ( my ( $key, $hash_ref ) = each ( %{ $dd{1} } ) {
    # $key == 2
    # $hash_ref == { 2 => { 3 => 'hi' }  }
}