How to output a structure sub-navigation of current page I've got a single structure menu for my entire site which consists of a title and a single related entry. I use that to output the main menu, which uses this code:

&lt;section class="top-bar-section"&gt;
    &lt;ul class="right"&gt;
        {% nav link in craft.entries.section('menu') %}
        &lt;li class="{% if link.slug == craft.request.getSegment(1) %}active{% endif %} {% if link.hasDescendants() %}has-dropdown{% endif %}"&gt; {# Checks if              the page link is the same as the slug of current page #}
            &lt;a href="{{ link.relatedEntry[0].url }}"&gt;{{link.title}}&lt;/a&gt;
            {% ifchildren %}
            &lt;ul class="dropdown"&gt;
                {% children %}
            &lt;/ul&gt;
            {% endifchildren %}
        &lt;/li&gt;
        {% endnav %}
    &lt;/ul&gt;
&lt;/section&gt;


On the top level pages, in their template they have a sidebar which should output the menu items in that main section - all singles. Is there a way to do this or do I need to create separate Structures for each section?
You first have to get the corresponding entry in your "menu" structure and then build your navigation upon that item.

Use the relatedTo() parameter for that. The entry entry model that you automatically get on that single template is the targetElement of that relation, but you should be fine using the less specific element property used with the short syntax relatedTo(myEntryModel).

{# Get the (one!) related entry from the "menu" structure #}
{% set menuItem = craft.entries.section('menu').relatedTo(entry).first() %}

{# Check if there are descendant entries #}
{% if menuItem.hasDescendants() %}

    {# Get entries to build the sub-menu #}
    {% set subMenu = craft.entries.descendantOf(menuItem) %}

    {# Output the sub menu #}
    &lt;ul&gt;
        {% nav link in subMenu %}
            &lt;li&gt;
                &lt;a href="{{ link.url }}"&gt;{{ link.title }}&lt;/a&gt;
                {% ifchildren %}
                    &lt;ul&gt;
                        {% children %}
                    &lt;/ul&gt;
                {% endifchildren %}
            &lt;/li&gt;
        {% endnav %}
    &lt;/ul&gt;

{% endif %}