More generally, though, my approach is to isolate each layer. Ideally, each level should be an array of objects or a hash of objects, which in turn is an array or hash of objects. Especially so if you have a number of operations carried out on the objects.If there are only one or two operations on the structures, I use a function for each layer:

sub process_frumptions {
    my ( $frumption_set ) = @_;

    for my $frumption ( keys %$frumption_set ) {
        process_one_frumption $frumption;
    }
}

sub process_one_frumption {
    my ( $frumption ) = @_;

    for my $barfloon ( keys %{$frumption->{'barfloon_gallery'}} ) {
        process_one_barfloon $barfloon;
    }
}
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Of course, you may have to profile and optimize, but most of the time I find the code runs fast enough, for some definition of "fast enough".