I have been known to collect a few such albums - usually live recordings.
I'm never sure about the various divisions between Metal, Heavy Metal, Hard Rock and Rock - but knew I was on the right track when my parents left the room
I stumbled across King Crimson's live album Earthbound:
I like it live because in this gendre they tend to wander off into lengthy intrumental solo's every five minutes and improvised performance to performance.
Others that had my elders scuttling away:
Deep Purple Live In Japan
Any live Yes album - Tales From Topographic Oceans.
Emerson Lake And Palmer - Welcome Back My Friends....
I'm sure that listening to such when the mood demands blows away a few mental cobwebs.