Long way:

run that file in the debugger and continue to the point where Somewhere::Deep::Within is loaded. Then, lets say, if that line 1234 is inside &Somewhere::Deep::Within::foo():

c Somewhere::Deep::Within::foo
c 1234
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The shortcut to that is to edit /usr/lib/perl5/Somewhere/Deep/Within.pm and add

$DB::single = 2;
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before that line and then you can continue to that point automatically...