This might have actually been a terrible idea.
Classic Trek: Season 1
Well, that happened.
Beginning the storied Star Trek tradition of rest and relaxation going horribly awry is this episode. Everyone's a little bit pervy, too, as befitting a holodeck-like episode, as McCoy jokes about being a peeping tom "in the line of duty," Yeoman Not-Rand conjures up Don Juan to fulfill her rape fantasies, and, not to be outdone, Captain Kirk eventually decides to spend his shore leave making time with an alien wax-works version of his ex-girlfriend. And to think, as a kid, I thought the creepiest thing about this episode was the White Rabbit!
The Animated Series
"Once Upon a Planet"
what is this i don't even.
Because someone in Starfleet apparently thought this was a good idea, the Enterprise goes back to 'the Shore Leave Planet' and the crew are very surprised when something goes wrong! This time - with some parallels to "Elementary, Dear Data" if you squint - the planet's central computer captures Uhura in order to gain control of the Enterprise. I'm making it sound infinitely more sane than the episode actually is, as you can probably guess by the above picture of McCoy and Sulu having a picnic with Alice, the White Rabbit, and a giant 2-headed dragon. They end up rescuing Uhura, and then they proceed with the scheduled crew shore leave, because like the holodeck, you just can't give it up even after it keeps trying to kill you.
TNG: Season 2
"When the train comes in, everybody rides."
This might be THE GREATEST EPISODE OF ALL TIME! Okay, I'm 95% kidding, but it's amazing. Riker, Worf and Data get trapped in an alien re-creation of a 'badly written book' called Hotel Royale. While Picard and Troi suffer through reading the novel on the ship to try and offer assistance, the away team navigates their way through a sea of crappy plots and clunky characters. It really is a holodeck episode even if they're not actually on the holodeck, right down to the traditional Holodeck Crack solution of "if you resolve the story, you'll be able to leave!" It's epic.
(caps, as always, from trekcore.com, gif from somewhere on the wild internets)