If you are playing Oracle of Ages on a Game Boy Advance (or a system emulating GBA hardware), you can access special GBA-exclusive rooms. These rooms are typically hidden behind seemingly solid walls or in unusual locations. To reveal them, you need to be wearing the GBA Time Ring, which is one of the 64 collectible rings.
When wearing the GBA Time Ring, certain walls will shimmer or appear slightly different, indicating a hidden passage. Bombing these walls will reveal a secret room, often containing a large amount of Rupees, a rare Gasha Seed, or even a Heart Piece. These rooms are a nice bonus for players on the correct hardware and add another layer of exploration for completionists.