This is certainly one of the most memorable episodes of all 3 seasons, to say the least. But it will always be remembered for the not-so-subtle demonstration of the dangers of breathing in foreign smoke through the lungs. You just might hear and see some unusual things if you do.
One day some sort of disruption in one of the pylons causes its crystal matrix table to stop working. This is unfortunate for everyone in the Land of the Lost because this is the clock pylon. This results in the sun not going down, so until someone fixes the problem, it will be forever daytime. Rick says he will go out and try and find Enik to see what exactly is going on. He leaves the cave at High Bluff to take the first steps on his long, strange trip.
Rick makes his way to the Sleestak caves, but Enik is nowhere to be found. Instead, the Sleestak are to be found and they capture Rick in a net. Meanwhile, Holly and Will see the whole thing happen on their pendants back at High Bluff. They set out to save dear old dad from the Sleestak for the umpteenth time.
Rick is led to the Library of Skulls, where a thick smoke makes its way into his lungs. Suddenly, Rick can hear the Sleestaks' words as if they are speaking English. He thinks, whoah it must be the smoke! The Sleestak tell him they think Rick did something to the clock pylon and caused the permanent daylight. Through the smoke, they show a video that shows him venturing into the pylon - but this is the future, not the past that they are seeing. Rick tries to convince them to set him free and fix the matrix table in the clock pylon, since the Sleestak can't go out in the sunlight.
Rick starts hallucinating. His speech becomes slow, soft, and very calm. He sees Will dressed as a football player, and Holly starts floating in the air. They all escape from the Library, and in the tunnels Rick sees a vision of Earth on a wall. He gets separated from the kids. Then he sees himself and the kids as cave-people sitting around a camp fire. He runs into Holly dressed as a 18th century British girl, and Will as a soldier boy. Whoah dude!
Finally, Rick makes it out of the tunnels. He thinks he's being captured again by two Sleestak, who turn out to be Will and Holly. Mr. Marshall seems to be in a euphoric daze. They make it to the clock pylon, and Holly gives him a blue crystal to put in the matrix table, and all is fixed. The sun goes down. But we'll never know if Will and Holly were really in the caves or not, or if Rick was just high as hell and imagined it.