I actually stood on the Mauna Loa caldera once when there was no activity, there was an officially marked trail that goes down right to the edge of it and there

I actually stood on the Mauna Loa caldera once when there was no activity, there was an officially marked trail that goes down right to the edge of it and there were signs that say something like "you can stand here at the edge for a short amount of time but go no further!" Although surely they close that trail off when lava activity is expected...