Moon

The is a planetary body orbiting the world. The moon was used by the first jinchūriki, the Sage of the Six Paths, through his and his brother's fūinjutsu. The Sage sealed the physical remains of the Ten-Tails after he used his Creation of All Things ability to divide its chakra into the nine tailed beasts. Hamura later took leadership of the Ōtsutsuki clan and decided to live on the moon in order to guard the Demonic Statue, though not before receiving instructions from his brother to wait for a full millennium and observe mankind.

Madara Uchiha, after awakening the Rinnegan, released the seal placed on the empty vessel of the Ten-Tails and summoned it back to earth. Madara's ultimate plan, that was later adopted by Obito Uchiha, the Eye of the Moon Plan, involved reviving the Ten-Tails through joining the other tailed beasts, becoming its jinchūriki, and then projecting his eyes onto the moon in order to cast his "Infinite Tsukuyomi": a perpetual, world-scale genjutsu cast on every living being on the planet. This would allow both Madara and Obito to control and unite them to create a world with neither war nor hatred, making themselves the rulers of the world but at the cost of eliminating free will from humanity.

Later, after the revival and subsequent battle with Kaguya Ōtsutsuki, Naruto Uzumaki and Sasuke Uchiha worked together to create a very similar satellite in her core dimension in order to re-seal her.

In The Last: Naruto the Movie, Toneri Ōtsutsuki dislodges the moon from orbit to collide it into the earth to punish humanity for abusing chakra. During his final battle with Naruto Uzumaki, the moon was nearly destroyed from their clashes and Toneri even cut the satellite in half. But later, thanks to Naruto's efforts, the Moon's orbit was later fixed and its shape later restored again to its original form.

Known Access to the Moon
In The Last: Naruto the Movie, there was only one way to access the moon. It was via a portal located inside an underground spring which seems to be covered with snow. The spring is unique because its water doesn't make anything which falls down to the spring wet. There is a different dimension in the portal which "bridged" the earth and the moon. The dimension is filled by many floating orbs, with some of them made from earthly material and many of them made from a quartz-like material that reflects the memories of anyone that passed through them and will trap them in their own memories if accidentally plunged into them. The dimension, somehow, collapsed near the end of the movie, and the "bridge" between the two worlds was severed.

Environment
In The Last: Naruto the Movie, the moon itself from outside seems to have a harsh, barren, and lifeless environment with a landscape consisting of many craters, canyons, and mountains. However, beneath the surface is a vast body of water, floating terrains, and a lush forest. One of the terrains holds the ancient ruins of the Ōtsutsuki's ninja village. However, unlike Earth, everything in here is floating away and reversed in position (the sky below and anything else above). Every living thing in the Moon's interior is supported by an artificial sun where the Ōtsutsuki's Tenseigan is stored.

There are some signs of living beings having existed in here. In the Moon's entrance there is a giant crab which is very skilled in Water Release and Yin Release techniques. Inside the Moon's interior there are many trees growing as well as insects (such as fireflies) and spiders. A large (now ruined) ancient city, where the Ōtsutsuki lived in the past, is also located here. In the core, a strange Golem-like being resembling Hamura resided. There is also evidence that cattle and agricultural crops are also there; in a scene, Toneri and Hinata dined on various foods, suggesting the moon dwellers were capable of sustaining themselves.

The artificial sun itself is guarded by a countless puppet armament. The only known access is via a special hand seal, which creates a circular opening. Inside the artificial sun there was Toneri's castle, the artificial sun's core, which consisted of a planet (where the Ōtsutsuki's Tenseigan is stored) is enclosed by a crescent-shaped planetary remnant formation resembling Ōtsutsuki's emblem. The core is also surrounded by numerous floating islands, with each island having a mountain, one of which houses Hamura's Shrine.

When the Energy Vessel was destroyed by Naruto and Hinata via their combined effort, the moon's movement was stopped temporarily. It also caused the artificial sun to disintegrate, causing darkness to engulf the Moon's interior. It also disabled the entirety of the puppet armament.

Trivia

 * Because of the moon's origin and it being the holder of the Ten-Tails' body, tailed beasts and subsequently their jinchūriki are affected by it, and much more so during a full moon.
 * According to Gaara, Shukaku relishes the opportunity to kill anyone in sight at any time because of its innate rage and blood-lust, but especially so during the full moon.
 * In the anime, Blue B, during his time as Gyūki's jinchūriki, noted that he would have trouble sleeping at night, especially during a full moon and at one point was shown to have to suppress a partial manifestation of Gyūki's tail after he had been staring at the full moon. Blue B was also shown to take sleep pills to help with this side-effect of being a jinchūriki.
 * During significant events, the colouring of the moon is usually red.
 * The Ōtsutsuki clan were able to adapt and populate the moon despite its harsh and barren condition. This was due to their unique anatomy and physiology, and to the creation of a habitable environment inside the moon using the power of the Energy Vessel.
 * The concept about Moon's interior and its environment maybe referenced from Earth's Interior in Jules Verne's science fiction novel Journey to the Center of the Earth, where the both place have exotic environment that capable to sustain any lifeforms supported by their respective core.