Looks like something supernatural is going on on the cover of Superman 236 (April 1971).
O’Neil, Swan and Anderson give Batman a cameo at the top of this story, as he and Superman finish rounding up a criminal gang. Batman is heading home for some sleep, but Superman does not sleep. He has invented a brainwave machine, and tries it out, but it seems to short out, and Superman finds himself among angels, helping them fend off devils at the gates of Hell. The angels tell him he has died, and order him to go battle the demons.
Superman goes along with things for a while, but the demons don’t seem very demonic, and in talking to them, they break through the hypnotic effect that the ‘angels” have subjected him to. Superman is really in the middle of a war between two alien groups.
The angels try to force him to stay on their side, threatening Batman, Lois Lane and Jimmy Olsen, but once Superman knows what is really going on, he helps the good aliens beat the bad ones.
Green Arrow and Black Canary guest in this issue World of Krypton story, by O’Neil and Giordano. They are fuming about the pollution destroying the environment, and so Superman shares with them a tale from Krypton.
A couple of decades before the explosion of the planet, another scientist had figured out what was coming. But when he tried to warn people, no one would listen. They were all really into just chilling and listening to singing flowers. Because the scientist kept ruining their groove, they sealed him up in the middle of a garden, until all he wanted to do was listen to singing flowers as well. Twenty years later, Krypton blew up.
It’s kind of a dumb story, really.