Assuming you know how to override theme templates (that would be a separate question) you can override the views_view_unformatted.tpl.php template and make your override something like this:
<?php if (!empty($title)): ?>
<h3><?php print $title; ?></h3>
<?php endif; ?>
<div class="wrapper-1">
<?php foreach ($rows as $id => $row): ?>
<div<?php if ($classes_array[$id]) { print ' class="' . $classes_array[$id] .'"'; } ?>>
<?php print $row; ?>
</div>
<?php endforeach; ?>
</div>
You could also override the views-view.tpl.php template instead and in the part that says:
<?php if ($rows): ?>
<div class="view-content">
<?php print $rows; ?>
</div>
<?php elseif ($empty): ?>
<div class="view-empty">
<?php print $empty; ?>
</div>
<?php endif; ?>
do something like
<?php if ($rows): ?>
<div class="view-content">
<div class="wrapper-1">
<?php print $rows; ?>
</div>
</div>
<?php elseif ($empty): ?>
<div class="view-empty">
<?php print $empty; ?>
</div>
<?php endif; ?>
It's up to you which way you want to do it.