Here's some interesting concept art and story details from an unproduced Star Trek film from 1976-1977 called Planet of the Titans. This version was written by Chris Bryant and Allan G. Scott. As you know we ended up with Star Trek: The Motion Picture, but before that there was Star Trek: Phase II, and before that there was this Planet of the Titans. The script was well received by the studio at first, but things lost momentum when Philip Kaufman was hired to direct the movie. He and Gene Roddenberry had conflicting ideas on the story and plot. Ultimately they couldn't develop a script that satisfied everyone so the writers left the project in the hands of Kaufman who explained,

My version was really built around Leonard Nimoy as Spock and Toshiro Mifune as his Klingon nemesis,” says Kaufman. “My idea was to make it less “cult-ish”, and more of an adult movie, dealing with sexuality and wonders rather than oddness; a big science fiction movie, filled with all kinds of questions, particularly about the nature of Spock’s [duality]—exploring his humanity and what humanness was. To have Spock and Mifune’s character tripping out in outer space. I’m sure the fans would have been upset, but I felt it could really open up a new type of science fiction.

This story is a very, very different take on the Star Trek franchise, and it would have changed every Star Trek movie that was made forever. It actually sounds like a very interesting story that would have worked much better had it not been placed in the Star Trek universe. I'm not sure how well it would have been received by fans. Here's a more detailed description of the treatment that Brant and Scott wrote,

Bryant’s and Scott’s treatment opened with the Enterprise racing to rescue a Federation starship in distress, called the Da Vinci. The Enterprise arrives too late—the Da Vinci has vanished but survivors are picked up. During the rescue Kirk is subjected to an electrochemical shock to his brain which brings on erratic behavior culminating in his commandeering a shuttle craft toward an invisible planet. He vanishes without a trace and Spock orders the Enterprise home. Three years later, the Enterprise, refitted, has a new crew. Spock has resigned from Starfleet in disgrace and is on Vulcan purging himself of his human half. The Enterprise, under command of one Captain Gregory Westlake, is ordered to the place where Kirk disappeared. Just as Spock theorized, a planet has been discovered, one that promises to be the mythical “Planet of the Titans”, the home of a lost race with super technology. However, the planet is about to be destroyed by a black hole. Whoever rescues the Titans will control the destiny of the universe. The Enterprise makes a detour to Vulcan to pick up Spock, who at first refuses to go. During his tests on Vulcan, however, Spock has his own death revealed to him, indicating that he must go with the Enterprise in order to fulfill his destiny. The ship arrives at the now partially visible planet and is trapped by the force fields surrounding it. Facing certain destruction, the Enterprise saucer separates from the rest of the ship, allowing the engineering hull to get free, while the saucer crash lands on the planet. The crew find the surface of the planet to be a wild and inhospitable with cities encased in walls of fire. Spock is reunited with Kirk, who has existed as a wild man with other trapped beings. When the landing party finally reaches the rulers of this world they discover them to be no benevolent Titans, but a lower and incredibly dangerous life form called the Cygnans. The Titans have long disappeared. In the attempt to escape from the Cygnans, who have transported on board before the saucer lifted off to rejoin with the ship, Kirk plunges the Enterprise into the black hole to save the Federation from the Cygnans. During the trip through the black hole, the Cygnans are destroyed, and theEnterprise emerges back in orbit around Earth. But it is Earth at the dawn of time and it is revealed that the ancient Titans were in fact the crew of the Enterprise!

Along with this whole new Star Trek universe comes a collection of concept art from artist Ralph McQuarrie, who also worked on several other films including Star Wars. These Enterprise designs are definitely different that what we are use to seeing. I think it would have been cool to see some kind of non-Star Trek version of this movie made. Check out the concept art and tell us what you think about this unproduced Star Trek: Plant of the Titans film.