Bunnymund's Warren is an underground oasis located somewhere below the Australian Outback seen in the film Rise of the Guardians. It is home to E. Aster Bunnymund and is where he prepares eggs for the annual Easter egg hunt.
Though it isn't mentioned in the film, the Warren lies beneath the Australian outback.
The Warren is a lush, tropical paradise. It is filled with hundreds of plants. There are also stone statues, almost hidden by moss, that look like totem poles except with rabbit ears sticking out of the top. There is also a purple river running through the warren the help to gloss the eggs before Easter.
At the edge of the warren are a set of seven tunnels that each lead to a separate continent: Europe, N. America, S. America, Africa, Asia, Oceania and Antarctica even though people hardly live there.
The warren is also guarded by giant egg statues that help to defend the smaller eggs that are destined to be found by the children on Easter.
Since the Tooth Palace crumbled away as did the belief in the Tooth Fairy, it can be assumed that the same would happen to the warren when the same happened to the Easter Bunny (though it is never seen in the film). With that, it can be assumed that the egg statues, the small easter eggs and all other magic that can be found in the warren come from the Easter Bunny himself.
Role in the Crossover
Much like North's Workshop and the Tooth Palace, the Warren serves as a base for the Big Four when they need to gather (preferably in the Seasons AU). Unlike North's Workshop (which holds many technological and magical armorments) or the Tooth Palace (which have the Big Four's memories, lest they be lost), the Warren does not seem to possess important merit aside from a calming atmosphere.
Comparison to the Books
Location and Characteristics
Bunnymund's lair in the novel is located in an underground base under Easter Island (much like the real Easter Island, but with bunny ears on the idol statues). The base is a series of rooms and tunnels lined with metal walls and passages, egg-shaped automotons of different sizes patroling the halls. There is a room fully dedicated to manufacturing chocolate of every possible (and impossible) brand and flavor, a room full of eggs from many different birds in his collection, and a carved tunnel (fit with a railway for an egg-shaped locomotive) that leads to the center of the Earth.
Role in the Books
Realizing that Pitch and his fearlings are harvesting lead from the Earth's core (an element that has not seen the light of the sun, giving it the ability to suck out light around it), Manny leads North and Katherine to Easter Island, home of the last surviving Pooka (and protector of one of the Relics of the Golden Age), where they enlist the help of Bunnymund (after a period of conflict) in the fight against Pitch and his army of fearlings, using his train and egg army to fight Pitch and defeat him