The Zoological Research Station, or The Hydra, is one of six stations built by the DHARMA Initiative. This station was revealed in "A Tale of Two Cities." The Hydra is located on a second island adjacent to the main island.
The purpose of the Hydra is relatively unknown. It was built as a zoological research station by the DHARMA Initiative, but the breadth of animals it once housed and the experiments conducted within the compound are not entirely clear. However, the Swan's blast door map does contain a reference to the "accelerated de-territorialization" of polar bears "through gene therapy and extreme climate change." The station was used and under the control of the Others, but was later abandoned after Sawyer and Kate were allowed to escape. Like much of the other DHARMA Initiative stations present on the island, the Hydra is in various states of disrepair. Unlike the other discovered stations, the Hydra is located on its own island roughly two miles off shore of the main island inhabited by the Oceanic survivors. According to Ben, this smaller island (temporarily dubbed "Hydra Island" for ease of reference) is roughly twice the size of Alcatraz Island in the San Francisco Bay.
The Hydra's precise location on Hydra Island is unknown, although it is likely on the side facing toward open ocean, away from the larger island. The compound appears to be located within walking distance to the beach, but the majority of its grounds reside within the jungle. Numerous open-air cages are in the compound, all of which appear to have been abandoned of their previous animal occupants. At least one large, three to four story tall building is present in the compound. Shower and locker facilities for DHARMA personnel are present, possibly in the aforementioned building, along with power generating equipment. The facility is further explored in the 2008 video game Lost: Via Domus. A large portion of the facility, namely the area Jack was held, is indeed underwater and is extensive in size and scope. However, according to executive producer Carlton Cuse, the video game is not canon. Thus the information and sights seen in it cannot be verified as existing within the show itself.
Several cages have been seen on the compound, two of which are present by the main building. Sawyer was kept by the Others in the same cage that once housed the polar bears seen in the jungles of the island. This cage is a type of Skinner box, giving positive reinforcement to the animal inside (in the form of food, water and an audio cue) for pushing a series of levers and buttons. Across from the former polar bear cage is another cage that housed a mysterious young man named Karl, who is Alex Rousseau's boyfriend. After an escape attempt, Karl was removed and Kate took his place in the cage. Audio/video cameras are scattered throughout the grounds with at least two trained on the cages that housed Sawyer and Kate. In addition to the cameras, speakers are mounted around the island as a public address system.
Part of the Hydra is possibly located underwater or has water pumped in from the ocean. This area that Jack was being kept in was referred to as an aquarium by him. It is not known if it is actually located in the ocean or if water is being pumped from the ocean into a land-based aquarium, but the latter seems to be more likely. Juliet said it once housed sharks and dolphins. A large room is present underneath or adjacent to the body of water and was used as a cell for Jack. There is at least one similar cell in the station. The room is split in two by an extremely hard, transparent barrier. An intercom is present on one side, but Juliet claims it hasn't worked for years. An audio/video camera is located inside the cell. The other side of the room from the cell contains a desk and an emergency button mounted to the far wall. The button apparently activates an emergency pumping system to prevent any flooding.
Jack's cell and the room on the other side of the glass partition are connected to a hallway. On one end of the hallway is a hatch that apparently opens into flooded space. Juliet and Ben warned Jack that opening the hatch would result in their deaths. A hatch on the opposite end of the hallway houses a surveillance room. Near this hatch is a ladder which is apparently the only usable exit/entrance to the hallway.
Inside the aquarium area is a surveillance room. It is at the end of the same hallway that Jack's cell is connected to and protected by a lockable hatch. The surveillance room houses two rows of three wall-mounted televisions, much like those found inside the Pearl. The televisions appear to only be connected to security cameras present in the Hydra, unlike the Pearl, but offer audio feeds in addition to video. Ben used the surveillance room to keep tabs on Jack, Sawyer and Kate.
To the right of the monitor wall is a second section of the room. Inside is a weapons closet. The closet contained at least three rifles, two Walther P38 pistols and numerous boxes of ammunition.
There is a large building that has an operating room and an X-ray machine somewhere in it, and likely other medical equipment. The fastest way from the aquarium to the operating room is past the cages. The operating room was probably once used to perform surgery on the animals once housed at the Hydra. Immediately above the operating room is a small observation gallery.
Several locations were used as The Hydra. The cages Kate and Sawyer were held in are props created specifically for the show. These cages were placed in Paradise Park, located in Honolulu, HI. Paradise Park was a tourist attraction specializing in exotic birds and botanical gardens until it closed in 1994. The buildings seen outside the cages in the show are the original buildings that were part of the park. The structure seen in "Not in Portland", where Karl was found being brainwashed and subsequently rescued from, is a former Omega station located in Kaneohe, HI. One of eight stations, the OMEGA Navigation System was used to help navigate nuclear bombers and submarines. The system became operational in 1971 and the Kaneohe station was operated by the United States Coast Guard until 1997 when the cost of operating Omega could no longer be justified due to the success of the Global Positioning System. Both the exterior and interior of the Kaneohe station were used in the episode.