- Method: Deep in the Clay Tunnel are the Underground Ruins. These
ruins are seldom seen caves which hold a massive puzzle. The first
one is the focus of the Pokémon Regirock and has you have to do a
puzzle that can only be known if you visit the place at Day and
night. The puzzle requires you to move 6 steps down from the
centerpiece and then move 9 steps right. Then select down to hit a
hidden switch. This changes the ruins so Regirock becomes available
-Serebii
I hope this is what you were looking ofr. Make sure you do all the steps right.