Ok, if you want to see the crater, goto the northface. Search on GPS for the Johnston Ridge Observatory. It’s incredible to see what happened to this mountain.
But on the South side of Mount Saint Helens, is a lava tube, that might be fun as a group halloween stunt, called Ape Caves. It is a old lava tube, that cooled. They haven’t lit the cave at all but the tube is like 12ft high. You need to bring your own lights. Highly recommend something very bright. A camera flash will help with photograph of the walls. It is $5, but the drive is so long that you will likely not be able to see the Johnston Ridge Observatory and Ape Caves in one day.
But there are several stops along the way to get a view of Mt Saint Helens.
There seems to be a retention wall where they hold back all the debris from the original mudflow, but I didnt see anything interesting to actually divert to.
You can see what seems to be either cooled lava with water flowing over it now (maybe it’s just hor the dirt looks now).
But Johnston Ridge Observatory is really where the incredible view is.