This has been answered so many times already, but I'll answer it again since your choice of topic subject might help others find the answer.
There are three places in Hoenn where one large rock is surrounded by six smaller ones. They are in the sandstorm desert, the ocean near Dewford, and the rainy forest, and a Ruins Maniac trainer stands near each (in fact, they're the only places you'll find those trainers.) These rock formations hide the Legendary Golems. To enter the secret chambers, however, you must first unlock them, a process which must take place on Route 132 and which requires a Wailord, a Relicanth, the HMs SURF, DIVE and DIG, and a working knowledge of Braille (most encyclopedias should offer translations.) Good Luck!