Bringing Nick to the SGC is the only way to save Daniel. Nick is the only one who can communicate with the "Giants" and convince them to return Daniel to our dimension.
While the rest of the team thinks Daniel has been vaporized or teleported, he has actually been shifted —he is invisible and intangible to everyone except Teal'c, whose Jaffa symbiote allows him to sense Daniel's presence. The Grandfather Connection [S3E21] Crystal Skull
Watching the episode, The Crystal Skull, right now. One of my Faves. Bringing Nick to the SGC is the only way to save Daniel
Fans often point out the production still on AppleTV that accidentally shows the skull without its visual effects. The Grandfather Connection Watching the episode, The Crystal
The episode kicks off when SG-1 discovers a massive Mayan-style pyramid on P7X-377. Inside, Daniel Jackson is drawn to a crystal skull that, upon eye contact, emits a blast of "lepton radiation."
The emotional core of the episode is Daniel’s relationship with his grandfather, . Nick is an eccentric archeologist living in a psychiatric institution because he claimed to have seen "Giant Aliens" through a similar skull in Belize decades earlier.