The Howling Stones, also called Wind Stones, are objects from The Legend of Zelda: Twilight Princess. These mystical stones are located throughout Hyrule. They are similar to the Gossip Stones in that both are engraved with the Sheikah Emblem. However, Howling Stones have a hole where the "eye" of the symbol would be on a regular Gossip Stone.
When approached, Howling Stones emit a strange whistle. If Wolf Link positions himself near one, he can howl along with the tune emitted by the stone. If Link successfully howls the song, he is transported to a strange world where a Golden Wolf can be found. He must then howl the tune once more. Once this has been done successfully, the Golden Wolf will jump from its platform and appear in a similar location on the mortal plain of Hyrule. Link, in his Hylian form, must then seek out the Golden Wolf, which will transport him to the Ghostly Ether. Here, Link finds the Hero's Shade. This mystical undead warrior teaches Link various Hidden Skills, necessary for Link to become the True Hero.
Interestingly, many of the tunes emitted by the Howling Stones are songs found in other Legend of Zelda games. Seven stones can be found in all, five of which emit songs from The Legend of Zelda: Ocarina of Time, The Legend of Zelda: Majora's Mask, or The Legend of Zelda: The Wind Waker. The Howling Stone found near Death Mountain whistles the "Song of Healing", the one in upper Zora's River sings the "Requiem of Spirit", the one in Faron Woods emits the "Prelude of Light", the Triforce-emblazoned stone in the Sacred Grove whistles "Zelda's Lullaby", and the one on the trail to Snowpeak sings the "Ballad of Gales". The Howling Stone in the Hidden Village, meanwhile, emits a variation of the Twilight Princess main theme, and the stone near Lake Hylia whistles a unique tune. While this last song in some respects resembles the "Goron Lullaby" from Majora's Mask, it is, in fact, only similar in the first four out of eight notes.
Although none of the Howling Stones are mandatory to complete the game (aside from the Triforce-emblazoned one), the Hidden Skills that become available to learn after using the Howling Stones can prove to be very useful against certain enemies. Also, it is worth noting that, no matter what order the Howling Stones are used in, the Hidden Skills are always taught in the same order.
Since the Howling Stones have the same emblem as the Sheikahs, this hints a deep connection between them (or more specifically, with the Hero's Shade A.K.A the Hero of Time). It's also possible the Howling Stones are somehow connected to the Ocarina of Time due to their mystical powers and same songs used to activate said powers.