Hi , thanks for your feedback.

Here's a diagram of what I more-or-less want to achieve (looks better
in fixed width font like courier):
-------- -----------
| | | |
5V | | 72V
| PIC---BBB |
| | | |
|------| ----SOL----

I have a 5V circuit with an intelligent PIC in it which will send out
a signal when the SOLenoid should be switched on. The solenoid needs
72V. The BBB is a big black box which, I suppose will either be a
transistor grouping thing or a relay of some sort.

The solenoid takes anything between 12 and 72V depending on how long
you have it working and how hard it should work. I have a 24V PSU that
plugs into the wall and converts 220Vac to 24Vdc. I think it's maximum
1A. I need something similar but in a 72V flavour.

And this is where I want to know, is this type of voltage getting
dangerous and which parts I should use for the BBB and the 72V
supplier.