I had created an Album, which is a container for mutiple Galleries. Simple enough. But then, once you had selected a Gallery, I wanted to display the Gallery description on the Gallery page above the thumbnails.

In the Manage gallery section you can type a description, but it didn’t seem there was any way to display that on the actual website.

So if you need to, open the file gallery.php which is inside the plugins directory, nextgen-gallery/view/gallery.php

Next, above the line
<div class="ngg-galleryoverview" id="ngg-gallery-<?php echo $gallery->ID ?>">
add this:
<h2><?php echo $gallery->title; ?></h2>
<p class="gallery-desc"><?php echo nl2br($gallery->description); ?></p>

This will give you an H2 with the Gallery Title, and then the description below it.