How to make next/prev links for entries circular/endless
I'm going to assume your project section is named projects, if it's not, replace it with you section name. 

Try this:

{% if nextEntry %}
    {% set nextEntryUrl = nextEntry.url %}
{% else %}
    {% set firstEntry = craft.entries.section('projects').first() %}
    {% set nextEntryUrl = firstEntry.url %}
{% endif %}

{% if prevEntry %}
    {% set prevEntryUrl = prevEntry.url %}
{% else %}
    {% set lastEntry = craft.entries.section('projects').last() %}
    {% set prevEntryUrl = lastEntry.url %}
{% endif %}

&lt;a href="{{ prevEntryUrl }}"&gt;Prev Project&lt;/a&gt;
&lt;a href="{{ nextEntryUrl }}"&gt;Next Project&lt;/a&gt;