Kutsugakure

is, as its name implies, a shinobi village built inside a vast and wide network of caverns within the Land of Mountains. The caverns over which the village was built originally housed a settlement of barbarians under the rule of a then notorious and feared warlord, who lived during the era of the Sage of the Six Paths. The hidden village is highly industrialised, not unlike Amegakure, with the whole settlement's power being supplied by geothermic energy generators, alongside being a market leader in the trade of precious jewels, minerals and fossil fuels, single-handedly rivaling even the whole Land of Earth in this particular sector, as stated by Tsunade.

Overview
Kutsugakure, not being the hidden village of a Great Nation, doesn't have an overseeing Kage. Instead, they have an oligarchic-type government, administered primarily by the village's noble clans' heads and elders. Mikuru Ryūrin claims this kind of government is a good way to keep the village united, since each of the clans have to rely on each other for mutual prosperity.

The village's location also offers considerable military advantage, shielding it completely from any external attacks. The village's infrastructure also prevents any attempts at caving in the mountain onto the settlement, rather conducting these cave-ins to strategic points in the caves leading to the surface, potentially blocking out invading shinobi or even trapping them inside the caves. The cave-ins can also be induced by the native shinobi for this specific purpose, though ambush tactics are often the preferred method, since the vast network of tunnels provides excellent ambush points for shinobi unfamiliar with the mountain's cave network.

The military advantages mentioned above are the primary reason why the village has been largely untouched ever since it's foundation shortly after the end of the Warring States Period, having only participated in the Third Shinobi World War, successfully fending off an invasion from the Land of Woods. However, due to its mostly defensive nature, Kutsugakure's shinobi, who often rely on ambush tactics as mentioned before, aren't very adept as front-line soldiers. To compensate for this, Kutsugakure possesses as their trump card the jinchūriki of Shiniyoku, a mythical tenth tailed beast created by the Sage.

Clans

 * Ryūrin Clan
 * Yomi Clan
 * Kongō Clan
 * Muenzuka Clan

Trivia

 * Kutsugakure is one of only two hidden villages from minor nations to own a tailed beast, the other being Takigakure, who owns the Seven-Tails, Chōmei.
 * Despite this, they're mostly feared for their ambush tactics and effective use of the local environment, instead treating their tailed beast as a last resort rather than a token of intimidation to other nations. Regardless of the village's reasons for keeping their jinchūriki and tailed beast mostly secret, this has undoubtly contributed to obscure Shiniyoku's existence further.