If I know what you're talking about, according to Serebii:
At the back of each chamber there is a little bit of Unown text which will give you a hint on what to do. If you follow the instructions, it accesses a new place in the ruins that holds 4 items and then another room with Unown text on the floor. The taskes are as follows
Upper Right Chamber: Use an Escape Rope
Lower Right Chamber: Use Flash
Upper Left Chamber: Have Ho-Oh in the front of your party
Lower Left Chamber: Have a Water Stone in your inventory
The two secret Unown (Unown ! and ?) can be found once all 26 Unown have been caught. You can talk to the Unown researchers and an entrance will open in the main cavern (pictured in the source) where you can catch the last two Unown.
Hope I helped. :)