Pokémon Gold and Silver/Ruins of Alph

'''The Ruins of Alpha house an interesting Archaeological Site that is over 1,500 years old. It's being studied by scientists trying to unlock its secrets. What could the mysterious writing that covers the walls mean? Until you can use Surf or Strength, you won't be able to explore the entire area to find out.'

Mysteries of the Ruins of Alph
There are four rooms in the Ruins of Alph, but for now, you'll only be able to get to one. Inside you'll find the first of four puzzles where you have to make a picture out of sliding tiles. Read the hint (Kabuto) on the right side of the stone tiles to help you slide the piece into position. Start with the corners, then the border, then finish with the inner pieces. When you solve the puzzle, a hole will open in the floor. You'll be dumped down to B1 where you'll fight the odd Pokémon called.

Catch at least three or more differently shaped Unown and when you get back out, one of the scientists will take you back to the lab and alter your Pokédex to include the Unown Pokédex so you can keep track of all the variations you catch. Access that in the option screen of the regular Pokédex. They'll be listed in the order that you catch them in.

If you catch all 26, the scientists will let you print them out on your Game Boy Printer. But note that all 26 variations won't be available until you've solved the puzzles in all four of the rooms.

Collect them all and win
There are different versions of the Unown Pokémon. If you catch one of each and talk to the scientists, they'll let you print out the Unown on your Game Boy printer. But you won't be able to catch more than A to K now; You'll need to solve the other puzzles to get the rest.

Return later on for more puzzles
You can swim to one of the sliding puzzle rooms, but the other two will require exiting from special areas within. The three new puzzles are much harder, since they're not symmetrical like the first one. Each one you solve releases more new Unown variations into the Ruins.

Natu, Smeargle and a Trainer
The thin strip of grass to the left of Psychic Nathan is one of the more overlooked Pokémon catching areas in the game. It's the only place that you can find either Natu or Smeargle, so don't leave without them.

To reach this place, go to the Union Cave and go one level down (ladder in the middle of the cave). Then go to the northwest corner of the cave and you will arrive. When you encounter a Smeargle, be careful not to kill it in one hit, as it is rare.