Otogakure

was the personal hidden village of Orochimaru, which was founded for the express purpose of collecting ninja for his experiments and his quest to learn all techniques.

Background
Initially, Orochimaru claimed that he founded this village so that skilled ninja would find their purpose in life without being beholden to the fickle and warmongering priorities of the Five Great Shinobi Countries. In actuality, Otogakure is not really a village, but a giant laboratory composed of various hideouts and bases scattered throughout the Land of Sound and various other countries. Otogakure's shinobi use a diverse number of techniques, which are mostly centred around the modifications resulting from Orochimaru's human experimentation.

Team Dosu, under Orochimaru's orders, entered the Chūnin Exams with the goal of killing Sasuke Uchiha while unaware their true mission was to be subjected to Sasuke's power after Orochimaru gave him the cursed seal. Later, Orochimaru tricked Sunagakure into helping Otogakure invade Konoha. Based on their map, Hidan and Kakuzu visited Otogakure while searching for jinchūriki.

Locations
Orochimaru set up many bases across the world during his travels. These bases ranged from usually inconspicuous underground hideouts with holes for entrances to more grand ones hidden on an island. All these hideouts were outfitted with laboratories where he and later Kabuto Yakushi would carry out experiments.

Land of Sound Base
The former headquarters of Otogakure up to at least Chūnin Exams, the stronghold was built below a tree. It has two markings on it reminiscent of a snake and what appears to be a snake's skull on the top-most part. This is where Orochimaru returned to after Hiruzen Sarutobi had sealed his hands and he remained here while he experienced the adverse effects of his rotting hands. This is also where Orochimaru kept the hand with his Akatsuki ring which Itachi Uchiha had severed. In the anime, when Naruto, Sakura, and Jiraiya infiltrated the hideout, they fought against Arashi, which lead to the hideout being destroyed.

Kusagakure Hideout
This hideout is located somewhere in Kusagakure or there about. Another hideout built entirely underground with the entrance being at the foot of a rock formation. Within the hideout itself are numerous rooms and a statue of a gigantic snake coiled up with candles in its eyes. This is where Sai attempted to carry out his secret mission to kill Sasuke Uchiha. This is also where Sakura and Naruto reunited with Sasuke after two years. The confrontation culminated with a portion of the hideout being destroyed. Orochimaru, Sasuke and Kabuto subsequently abandoned it.

Southern Hideout
The is located on an island in the middle of an ocean somewhere possibly off the coast of the Land of Waves. It was filled with prison cells and wardens were also employed to keep the prisoners in check, one such person was Karin who later join Sasuke's team Hebi.

Northern Hideout
The is one of Orochimaru's grander hideouts in terms of size. It is one of the hideouts that Orochimaru used to conduct his human experiments with the cursed seal. Jūgo was kept here since he was the origin of the cursed seal. After Orochimaru's demise, Sasuke freed Jūgo from here and had him join his team.

Eastern Hideout
The is one one Orochimaru's undergrounds hideout. It has a mouth of a snake for an entrance and several snake-like candle-holders on the walls. This was where Orochimaru tried to take over Sasuke Uchiha's body. Sasuke, however, was the one to take over Orochimaru's body instead. It was also filled with large glass cylinders with liquids in it. Here was where Suigetsu Hōzuki was kept and experimented on until Sasuke Uchiha freed him from confinement. Upon returning to the hideout, Suigetsu found a secret chamber after Jūgo had attacked him and broken a false wall. Within his secret chamber, Suigetsu found a scroll detailing how to summon Shinigami and take back the contents within.

Island Laboratory
This laboratory is built into the side of a small island and is a medical laboratory created for Kabuto to use. The lab is covered in medical equipment, ranging from scalpel to test-tubes. The lab's most unique feature, however, is the large blood extracting machine in the centre of the room, which Kabuto used to transfuse Orochimaru's blood into himself after his apparent defeat. One of the room's massive walls is covered in ceiling length shelves stacked full of jarred experiments, books, scrolls, crates, and tools.

Demon Island Laboratory
This laboratory, appearing in the anime-only Kaima Capture Mission, is located in the Demon Island of the Land of the Sea. It is an experimental laboratory with many transgenic creatures contained in test pillars. Some time before the start of the series, Amachi, the lead scientist, and Orochimaru terrorised the people of the Land of the Sea by kidnapping the citizens for their deadly experiments, which included making the ultimate underwater ninja, an idea later abandoned by Orochimaru.