You find them after killing frost giants. The ruby one is behind an altar in the inner sanctum, emerald is up high in some large falmer camp, and the other two are near the river. Sorry I don't remember clearly; you're right, FV is massive. I wish they would have given us some additional sub-locations. Same thing with the Soul Cairn.
Seriously! Forgotten Vale isn't hard to traverse what with the way shrines, it's just hard to navigate. Whereas the Soul Cairn is both hard to traverse and harder to navigate (everything looks the same!). They really needed to have these places on the world map like the giant's grove with the shrine of Malacath or Hag's End.
The Ruby paragon takes you to a small, enclosed forest wherein you can kill a flamer warlord for Auriel's Shield, a matching companion for the bow (Coupled with Dawnbreaker you can almost RP a Paladin version of Link).
The paragons take you to areas where some of the four Snow Elf books are found, you can return them to the Orc librarian at the College for 1000 gold & a translated version.
The paragon teleporter is down the cliff from the third way shrine, the one just after the dragon lake. The teleporter looks like a ruined Falmer gateway to the left of the river (looking north). The small activation node sets the ruin apart from all of the other ones.
Good hunting!