A great Neal Adams cover, and a fairly good story, by Dorfman, Andru and Esposito, in World’s Finest 183 (March 1969).
Two members of the “Time Patrol” show up, accusing Superman of grave crimes against humanity. At some point in the future, Superman will become possessed by red kryptonite, and set off a devolution machine, creating a Planet of the Apes. They bring Batman to the future and show him their world.
At the UN, they dramatically unmask, showing that they themselves are apes. The UN votes against Superman, and plans are made to lobotomize him.
Superman then reveals that the apes are really Brainiac and Luthor. Batman had not travelled to the future, but to the film set for Planet of the Apes. Batman didn’t figure that out for himself, which is shameful.