Drupal's taxonomy system is wonderful in many regards, but it has major FAIL issues. One of those is the navigation of vocabulary term pages where the vocabulary has a hierarchy. By default the taxonomy system uses pages at "example.com/taxonomy/term/%tid" to display teasers for nodes having the given term. Ideally these pages would enable browsing around in the hierarchy of terms in the given vocabulary, but that's not the case. Fortunately the fix is pretty simple though rather obscure.
The ideal in my mind is for the vocabulary term page to display these items: