Your loop looks ok, but maybe we need to see your dumper output: 
use warnings;
use strict;

my %lengths = (c1 => {z => [1..5]});
for my $coord (keys %lengths) {
   for (@{ $lengths{$coord}{z} }) {
      print "$_\n";
   }
}

__END__

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A good reference:

In reply to Re: Help with array ref in hashes by toolic
in thread Help with array ref in hashes by diyaz

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