The Japan episode ends in a big one for Karl, he reaches the summit of Mount Fuji, coming up with the Pilko Pump Pants in the process.
A small addition that makes it cooler is that, before he reaches the top, he talks rather irately about the things he hasn't accomplished — he hasn't gotten married, he still hasn't put up all the wallpaper in his home. "The only thing I ever reach the end of is a packet of biscuits, that's just who I am." Then he finally gets to the top. A few moments after this he mentions that he still feels awful, but the calm in his voice when he says that he made it is really great.
The Jordan episode of the first season. Despite going through hell to get there, he finally gets to the ruins of Petra. That's not the awesome part. The awesome part is when Ricky and Steve stick him in a cave across from the ruins, thinking it will just make him upset and make him feel dumb for stating that he felt Petra would be pretty for the neighbors, but terrible to live in. Not only does he love the cave, but he ends up proving his point (at least personally) to Steve and Ricky, which Karl uses as a Take That! moment towards them.
In the last episode of the third series Warwick's synusus act up and he has trouble going up the hill to a temple. About a quarter of the way there he stops and considers giving up. He does not want to cheat by using the seat-carrige and he wants the experience of earning it, so Karl gives him some tough love and eventually Warwick makes it to the top and does not regret it. Even better is Warwick is the one to do a falling at the end of an episode so in the end Ricky points out that Karl was worried Warwick's size would be a handicap when in the end Warwick has more guts for exciting activity.