How do you get to the other puzzles?

You have to solve each puzzle in the Ruins of Alph. Each puzzle causes more unown to appear in the underground portion. You just have to keep hunting for what unown you are missing. It takes a long time.

First, make sure you have solved every one of the sliding stone panel puzzles and gotten into the secret rooms behind the inscriptions on the back walls of each puzzle chamber. Once you have done all that, you need to collect all 26 original Unown forms, and then fill the Unown Report as much as you can by talking to the scientist by the bookshelves. Once that's done, go back to the chamber entrance; you'll see an inscription at the back of the chamber glowing. When you attempt to read it, a scientist will walk in, and you'll end up back at the research house. Finally, go back to the chamber entrance and collect the '?' and '!' Unowns, and grab the last pages of the report accordingly.

Cross stinger is right just note that some of them are pretty tough it took me a few days to finish them all

U can get to the last two sliding puzzles and secret puzzle rooms by taking an indirect upper route through union cave. U need to go through the cave each time you go to do a puzzle.