Hello Francisco,
Vagrant guest is created in a two step task
first step, download the base box,
second step, create the guest from the base box.
if you do this manually, the commands are like this:
vagrant box add user/box
vagrant up
the first step will download the box, and put it on the
HOME/.vagrant.d/boxes/<somwhere>
and the second will use this base box to create the end guest.
Vagrant is also smart, if the first time you do a vagrant box, it will
download the box, and save it on the boxes folder, and then create the
guest from the template
this is why, after a vagrant destroy just the guest, and not the base
box is deleted.
vagrant box list
vagrant box -h
are the commands that apply on boxes, so there is how to delete old
boxes when you want to do it.
hope this clarify the part of boxes/destroy
Alvaro