Stay to the wall and walk one lap.
the other answer is a lie!
i think it is by the entrance at Route 217 to Mt.cornet. The cave with the two rocks is where you catch it.
ewan q
u have to do one lap around the wall
you can find regiice near the dewford town,surf northwest.
come and see
The code is OPEN
You go to the ice cave and find the area where there are to golems, a medicham and a dusclops go and break the rock which blocks a cave and smash the rock closest to the entrance. Go down the hole and you will find regiice there.
Firebug.
The entrance is on the right side of the building on the bottom you have to use the crowbar to open it.
be smart and you will figure it out
an open area in front of a structure's entrance.