This really isn't much of a game, but more of a tech demo for the technical geeks. This little gem includes most elements found in its complete game, Half-Life 2. Originally planned as a section of the Highway 17 chapter of Half-Life 2, this unused concept was scrapped, possibly due to time constraints or maybe based upon the fact that this game is a prototype all on its own.
This demo details various visual and graphic capabilities that are found in that said complete game. All the while, this ''game'' just shows how immensely strong the Source engine is, considering it was pretty new for its time back in 2004, and how it would become the most essential game engine to date, what with various Valve and 3rd party games being built on top of this incredible engine. The most clear concept that is shown off is the high dynamic range lightning that is now most commonly used in nearly all of Valve's games.
There isn't much of a story or a narrative in this demo, you're none other than Gordon Freeman, who is stranded on a lost coastal cliff, (The clue is in the title.) that you must climb up to destroy a Combine artillery launcher in a monastery, which is rebelling and attacking a nearby town. Though this is just one massive chunk of a technological demonstration, it has several story elements that didn't make the cut in the final game. As a result, this level received a good response from the community, as if the fans haven't been missing anything at all.
While I would say, this game is very interesting if you love to dig down and unearth various unused game content and maybe discover a little of the history that had been closed.