Discovered and used long before by Bruce Wayne's ancestors as a storehouse as well as a means of transporting escaped slaves during the Civil War era, Bruce himself rediscovered them when he fell through a dilapidated well on his estate.

Much like Superman's Fortress of Solitude, the Batcave serves as a place of privacy & tranquility where Batman can be himself.

Upon his initial foray into crime-fighting, Wayne used the caves as a sanctum and to store his then-minimal equipment. As time went on, Wayne found the place ideal to create a stronghold for his war against crime, and has incorporated a plethora of equipment as well as expanding the cave for specific uses.

The cave is accessible in several ways. It can be reached through a secret door in Wayne Manor itself, which is almost always depicted as in the main study, often behind a grandfather clock which unlocks the secret door when the hands are set to the time that Bruce Wayne's parents were murdered, 10:47. Alternately, the study entrance has been shown to be behind a bookcase which slides to the side when a secret button is pushed, revealing the "Bat-Poles", which allow Bruce Wayne and his ward to change into their Batman and Robin costumes en route as they slide down to the cave.

Another secret entrance, covered by a hologram or a camouflaged door, allows access to a service road for the Batmobile. Another alternate enterance is a dry well, highlighted especially during the Knightfall storyline. At one point, Tim Drake and Dick Grayson use the dry well to get into the cave, which they had been locked out of by Jean Paul Valley during his time as Batman.

The cave's centerpiece is a supercomputer whose specs are on par with any of those used by leading national security agencies; it permits global surveillance and also connects to a massive information network as well as storing vast amounts of information, both on Batman's foes and his allies. A series of satellite link-ups allows easy access to Batman's information network anywhere in the globe. The systems are protected against unauthorized access, and any attempt to breach this security immediately sends an alert to Batman or Barbara Gordon. Despite the power of Batman's computers, the Justice League Watchtower is known to have more powerful computers (composed of Kyptonian, Thanagarian and Martian technology), and Batman does occasionally use them if he feels his computers are not up to the task.

Additionally, the cave contains state of the art facilities such as: crime lab, various specialized laboratories, mechanized workshops, personal gymnasium, a vast library, parking, docking and hangar space (as appropriate) for his various vehicles as well as separate exits for the various types, trophies of past cases, a large bat colony, and a Justice League teleporter. It also has medical facilities as well as various areas used in training exercises for Batman and his allies.

The cave houses Batman's vast array of specialized vehicles, foremost being the famous Batmobile in all its incarnations (mostly for nostalgia as well as for contingencies, as all are serviceable and in excellent working condition). The 1990s animated series gave rise to the idea that Batman keeps a fleet of regular cars of various models and utility vehicles such as an ambulance as well when the Batmobile would be too conspicuous for a mission. Other vehicles within the complex include various motorcycles, and various air and watercraft such as The Bat-Wing, a single occupant supersonic jet. Another vehicle found in the Batcave is the subway rocket, debuted in Detective Comics #667, during the time when Jean Paul Valley was substituting for Bruce Wayne after Bane broke his back. It let Batman get into Gotham very fast, and could electronically clear a path via Gotham Rail.

The cave is sometimes powered by a nuclear reactor, but most often by a hydro-electric generator made possible by an underground river.

Since No Man's Land, Batman has incorporated safeguards against earthquakes and even a potential nuclear catastrophe, outfitting the cave as a virtual bomb shelter or an enhanced Panic Room.

The New Cave is a self substaining underground bunker.
Main Level - Batcomputer
Sub-Level 1 - Guest quarters for Batman's closest allies.
Sub-Level 2 - Gymnasium and shooting range
Sub-Level 3 - N/A
Sub-Level 4 - Harold's old bunker
Sub-Level 5 - Solar and Hydrogen power generators
Sub-Level 6 - Storeage for the Batboat and Subway Rocket
Sub-Level 7 - Only Batman knows what the purpose of this level is for
Batman has also, from time to time used satellite caves. Batman first built these caves after his encounter with Bane. He makes sure that they are well stocked for emergency use.

Various Looks at the Batcave both Old and New: