Silent Realm

The Silent Realm is a supernatural region in SS undefined. Link accesses the realm by thrusting his sword on a Trial Gate, found by dowsing an area known to house a portal. The Silent Realm is a test forced upon Link by the Goddesses so that he can claim proof of his spiritual growth. Upon completion of each Silent Realm, Link is awarded a sacred treasure which allows him to traverse a region previously unexplored towards locating the Goddesses' Sacred Flames. The treasures garnered by the Silent Realms include the Water Dragon's Scale at Faron Woods, the Clawshots in the Lanayru Desert, the Fireshield Earrings at Eldin Volcano, and the Stone of Trials at the last Silent Realm in Skyloft. The Sky Keep provides access to three isolated areas of the Skyloft Silent Realm where the individual Triforce pieces are located.

Features
After playing the appropriate goddess' song upon the mark, Link will be taken into an alternate dimension of the current world he is in, defenseless, and his spirit will have separated from his body. To prove his spiritual growth and leave the Silent Realm, he will have to collect all fifteen Sacred Tears scattered about the region, and store them in his Spirit Vessel, all without the help of Fi. Link begins within a protective circle, though, the moment he steps from it, the realm's knight-like overseers, the Guardians, will awaken and give chase. To emphasize the stealthiness required of Link in this trial, Watchers, ghost-like lamp-carrying beings, will be patrolling the area. Guardians exist in a dormant state as long as Link remains vigilant in collecting Tears. Guardians will awaken after one of three events occur: Link does not collect a Tear for 90 seconds; he is spotted by a the lamp light of a Watcher; or he stumbles upon Waking Water. The nine-petaled flower at the top of the Spirit Vessel acts as a timer; each petal represents 10 seconds, and when all petals are shed, the Guardians awaken and begin to chase after Link. Every time the Guardians awaken, the stunning effect of the Tears is canceled until Link manages to find another. After only one hit from any Guardian, Link must restart the entire trial. The locations of the Tears Link has collected will be marked on the Map, easing future attempts if Link fails the trial.

To help him find the remaining Sacred Tears, Link can pick up a Light Fruit to reveal their locations, in a fashion similar to that of beacons, for 30 seconds. After Link rescues all fifteen Sacred Tears, he must safely return to the mark without being noticed by the Watchers.

Dusk Relics are strangely abundant in Silent Realms, and are the only Collectibles that exist at all during these events. Dusk Relics are needed for several upgrades. If Link does not receive the amount of Dusk Relics he needs after completing all of the Silent Realms, he can explore them again in Lanayru's Lightning Round to collect more.

Theory
The Silent Realm is theorized by some to be the Sacred Realm, due to the fact that both of them are mirror realms of the surface world where the Triforce is hidden. On the other hand, the Silent Realm is mentioned as a place where the hero's mind will be tested and thus can be accessed spiritually, whereas the Sacred Realm can be accessed physically by anyone; it is possible, however, that this mechanism was used to prevent the realm from changing to reflect the hero's nature, thus compromising the trials he needed to undertake. It is also possible that the Silent Realm itself is simply the Sacred Realm reflecting Hylia's inner nature, as, while she was unable to use the Triforce, she was presumably the last to touch it before Link.

When Link reaches the Sky Keep, in order to obtain any part of the Triforce he is sent into an area of the Skyloft Silent Realm where that part of the Triforce is hidden. This supports the theory, because maybe the Sacred Realm is a quiet place as a reflection of Link's kind heart. Also, the timeline placement of Skyward Sword is before the events of Ocarina of Time. This is important, because the Sacred Realm hasn't been corrupted by Ganondorf yet.

Another thing that may support the theory is that when Link gets the last part of the Triforce, everything around him in the Silent Realm turns golden. In it was said that the Sacred Realm reflects the heart of someone who has the Triforce, and in  the Sacred Realm was known as the Golden Land, by people who didn't know Ganon had corrupted it.

Finally, the depiction of the Sacred Realm in the shows several floating islands in the sky with the Triforce above a large island in the center. This depiction of the Sacred Realm could be compared to The Sky and Skyloft.

Trivia

 * The ethereal, quiet presence of the Silent Realm is what sets it apart from the natural world; it is slightly reminiscent of the Twilight Realm regions from.
 * It's also very similar to the Temple of the Ocean King from, as both have time limits and feature invincible patrollers that make Link faint with one attack, flying enemies that summon said patrollers, and mysterious water that also summons them.
 * The background music of a Silent Realm is a softer, more ethereal version of the corresponding area's usual theme.
 * Before release, the Silent Realm was known as the Siren Realm before it had a name change. This explains why the hylian letters around the protective circle in the Silent Realm spell out the word SIREN.