Stargate SG-1's first season doesn't tend to have the greatest reputation - along with the first seasons of any number of genre shows - but along with several undoubted clunkers, it also threw out a few classics, and I think this is one of them. Not only does it feature a planet that resembles neither Egypt nor Canada (the dramatic medieval-looking castle on a cliff by the sea is rather fab-looking) but it is probably SG-1's most romantic episode. SG-1 produced several romantic episodes over the course of ten years, most of them tragic, but few could match this story, in which Daniel discovers that a man called Ernest went through the Stargate and never came back fifty years previously, and reunites him with his long-lost finacee Kathryn, who owns the Stargate and who kick-started the programme.
When I grew up watching Star Trek, it used, from time to time, to produce episodes in which our heroes were flung to the far sides of the galaxy by some super-powered alien thing or negative space wedgie and someone would dramatically state how far away they were and explain that it would take decades (more rarely centuries) to return home. Of course, by the end of the episode, they were all safely back in the Alpha Quadrant (TNG's 'Q Who' is probably the best, in which Starfleet are introduced to the Borg). Like Voyager and Farscape, this episode highlights what might happen if our heroes didn't make it back by the end of the episode, but unlike those shows, in which the overall arc required that they get home at some point (even if they don't stay) Ernest, in this episode, is actually stranded for five full decades. Also unlike those shows, there is no possibility of Ernest travelling for a long time until he gets home - he is literally stuck and has to wait for rescue.
Unusually for Stargate, the classical references in this episode are not literal - Latin being used as a language, the ancient gods turning out to be aliens - but metaphorical. There are a few references to various things that, in the world of Stargate, are literally true, including Ra being in Heliopolis and Thor being an alien, but the primary ancient reference is that of the title, which is from a well known Greek myth. Tantalus was once a favourite of the gods and used to dine with them, but he committed a terrible crime (which varies from source to source, but usually it's giving mortals nectar and ambrosia, the food and drink of the gods, generally revealing the gods' secrets to mortals, or serving the gods his own son as dinner to see if they tasted the difference) and was sent to the Underworld for eternal punishment. The punishment itself also varies, but it is always along the same theme, of something being just out of reach. The most common versions are that he is standing in a pool of water that drains away when he tries to drink, or standing just beneath a bunch of fruit that is just out of reach (in the Odyssey, Homer gives him both).
Ernest got stuck the wrong side of the Stargate because he was reaching for something that was just out of reach, and has come to regret it. He tells this myth (pool of water version) to Kathryn as he explains how much he wishes he hadn't come. Meanwhile, Daniel has become fascinated by an alien version of the Rosetta Stone which he is trying to interpret - an inscription in several langauges (including Norse runes) with a central version in a language made up of diagrams of elements of the periodic table (used as a universal language, which kinda makes sense... I think). But, of course, our heroes have arrived on the very day that a castle that has stood for millennia is about to come crashing down into the sea. So Daniel has to leave, to save his own life. He wants to take the risk and stay, but Ernest persuades him that he shouldn't throw his life away on something that will probably remain forever out of reach. The title could also refer, of course, to Ernest's position, stuck just the other side of the Stargate for fifty years, unable to get through.
It's nice to see SG-1 using myths as metaphor for a change. Of course, any show set in any time period on Earth can do that, and SG-1 usually has more exciting things in mind for its mythical characters (seeing them in the flesh, for one thing). That's the nature of the show and there's nothing wrong with that. But one of the reasons people value mythic stories is for their potential for interesting metaphors - a simple, familiar story can resonate more and have a greater emotional effect on people than something long and complicated, or entirely unfamiliar. Myth in science fiction doesn't always have to be aliens and pyramid-shaped spaceships; sometimes, as in any other genre, it can be all about the emotion.
Kathryn and Ernest go home together at the end, of course. Awwwwwww. (Sniff).