I remember watching a Twilight Zone episode called The Parallel (1963) in which an astronaut returns to Earth from space only to find the world he left behind is not quite the same as the one he remembers. The plot of Doppelgänger (Journey to the Far Side of the Sun) follows a very similar path.
In Doppelgänger, scientists discover a planet in the same orbit as Earth’s but located on the exact opposite side of the Sun thus rendering it invisible from view. The European Space Exploration Council then sends two astronauts on a 6 weeks return journey to investigate the planet but are suspicious when the spaceship returns in only half the time. Astronaut Colonel Glenn Ross then makes the startling discovery that he may, in fact, have landed on a counter-Earth that is the exact mirror image of his own planet.
Although parts of this sci-fi tale require a major suspension of critical thinking, Doppelgänger is nevertheless an enjoyable experience harking back to a different era in film-making. The modelling and special effects were quaint, while the theatrical acting, psychedelic effects and dramatic music help create a vintage, surreal sci-fi experience.
If that isn’t enough, plenty of entertainment can still be had from watching a 60’s style vision of the future, along with its whacky cars, sliding doors and world where everyone either wears a turtlenecks sweater or a mini-skirts.