How to move an element into another element?

I would like to move one DIV element inside another. For example, I want to move this (including all children):

<div id="source">

...

</div>

into this:

<div id="destination">

...

</div>

so that I have this:

<div id="destination">

  <div id="source">

    ...

  </div>

</div>

Source: Tips4all