The moon orbiting P5X-777 was intended to be a utopian paradise. An ancient stone key had been found over 80 years ago in a pharaoh's tomb in Egypt, wrapped in a scroll with writing on it that no Earth linguist could decipher. The scroll contained instructions to use the stone to access the power of the gods, and told of an alien utopia.
Long ago, an advanced race, probably the Furlings, gave up advancements and formed a small isolated and secret utopian community. They sent out representatives to meet and evaluate people from all over the galaxy, to offer them a chance to join them, and the scroll and stone had been the invitations. The stone key dials a combination lock within the temple on P5X-777, which activates a doorway and transports visitors to the paradise on the planet's moon.
When O'Neill and Maybourne were accidentally transported there, they discovered ancient deserted ruins, and the skeletal remains of the inhabitants. O'Neill determined that a Goa'uld had been inadvertently invited to Paradise and had brought with him a plant which causes symptoms of paranoia and hallucinations when eaten. The Goa'uld intended to use the effects of the plant to force the people to serve him, but instead the inhabitants separated into two camps and fought each other until the entire society was wiped out. With no stargate or means of communication, O'Neill and Maybourne were stranded on the deserted utopia for almost a month, both suffering the hallucinogenic effects of the plant. When SG-1 was able to determine where the doorway had sent them, O'Neill and Maybourne were rescued by ship.
Episode Reference: Paradise Lost