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. 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, which will 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.

Known Access to the Moon
In The Last: Naruto the Movie, several ways are shown to access the moon:
 * Via a portal located in a random 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 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, near the end of the movie collapsed, and the "bridge" between the two worlds is severed.
 * Via a boat-like device that used by Toneri. Anyone who rides it will be safely transported with the device to the moon.
 * Via an unnamed technique which was used by Toneri's puppet. By forming a tiger seal, it will open a circular portal and anyone which passes through this will be teleported to the moon.

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 somehow are able to adapt and populate the moon, despite its harsh and barren condition (mostly due to their unique anatomy and physiology). This is due to creating a habitable environment inside the moon using the power of the Energy Vessel.