Silent Realm

The Silent Realm is a supernatural region in Skyward Sword. 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 an infrequent test forced on 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.

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 safety 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 sometimes compared with the Sacred Realm, due to the fact that in both realms the Triforce is hidden. The difference between both of them is that The Silent Realm is mentioned as a place where the hero will be tested by the goddesses, while the Sacred Realm is referred as a place where the Triforce lies. This clearly contradicts the theory, but at the same time the statement supports it, because when Link enters the Silent Realm, the region is suddenly transformed into a quiet place, similar to Ganon's Dark World. Something that also contradicts the theory are the Guardians. Those Guardians are sent by the Goddesses to prove the hero and obviously, they have been never mentioned during the events of the Imprisoning War. But, when Link reaches the Sky Keep and obtain any part of the Triforce, he is sent into a dimension (and a room) where that part of the Triforce is hidden. That room is similar to the Silent Realm Link visited before, but this time, there are no Guardians at all, because the hero already proved himself with the goddesses. This highly supports the theory, because maybe Link's Sacred Realm is reflected as a quiet place due to his intentions to use the Triforce are not evil instead of Ganon's.

Something that also supports the theory, is the fact that when Link is sent to the Silent Realm, he can't use any of his weapons. At the ending of Ocarina of Time, Ganondorf is sealed in the Sacred Realm, and also he's not wearing any weapons.

Also, the timeline placement of Skyward Sword is before the events of Ocarina of Time. This also is important, because the Imprisoning War hasn't happened yet.

Finally, if you look at the depiction of the Sacred Realm as depicted in the Link to the Past manual, it shows several floating islands in the sky, the main one of which has the exact same silhouette as Skyloft. But the color palette of the image is all blue and orange, just like the Silent Realm. This matches the fact that the Triforce (which is said to be housed in the Sacred Realm) can be found in the Silent Realm version of 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 Twilight Princess.
 * 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.