The island is surrounded by a sea of fire on one side and icebergs on the other. In the center, there is a hole where seawater flows into it, which separates both halves of the island and has sharks living within. This hole has fierce wind and currents running across it. As touched upon by Robin, the extreme temperature differences between the ice and magma lead to an equally extreme difference in air pressure, forming massive gale-force winds. The lake was originally a crater formed at the epicenter of Akainu and Aokiji's death match and then later filled with seawater, though the aftermath of the duel did leave behind patches of burning and frozen waters in the lake. The entrance is bolted with a danger sign, hazard stripes, and the logos of the Marines and World Government. The external border is heavily fenced in and inside lies a military base.
The Burning Lands is the eastern half which was most affected by Akainu's Devil Fruit ability. Before the poison gas incident occurred, it was once a military base of the World Government where the island's main Dock was located, but the disaster caused the base to be abandoned and the entrance bolted shut with hazard warning signs. A fiery sea surrounds the burning lands which was caused by the aftermath of the duel, making it impossible for ships to dock at the main entrance. Due to the area's volcanic heat, all of the buildings were melted and deformed, and the streets riddled with lava pits. A large partially melted skull is located near the melted base. The artificial dragon created by Dr. Vegapunk was roaming in the melted base before it was slain by the Straw Hats. Caesar Clown keeps his pet, Smiley, confined in a warehouse on this half of the island.
The Ice Lands is the western half which was transformed by Aokiji's Devil Fruit ability. Four years ago, this half was the area where the poison gas incident originated from, causing the original inhabitants to flee the island. Since the duel, this half has become a frozen region with gigantic ice mountains and freezing winds, surrounded by numerous drifting icebergs. The Yeti Cool Brothers operate as assassins in the mountains, taking orders from Caesar.
The Ice Lands also contain a harbor full of captured ships. This area is not fenced in like the Burning Lands since the waters around the Ice Lands are less dangerous than the burning waters, making the Ice Lands a reasonable area for ships to dock, provided they avoid the icebergs.
The Ice Lands also house numerous laboratories and underground facilities which were once used in chemical warfare research headed by the Government's leading scientist, Dr. Vegapunk. The labs stretch across the mountain sides. Most of them were destroyed by the Poison gas fallout and few remain standing after the admiral duel.
When the island was a secret research station, it was home to hundreds of researchers, the most noticeable being Dr. Vegapunk and Caesar Clown. Vegapunk in his spare time created artificial dragons on the island that were used as guards and pack mules. The island also held prisoners who were brought to the island to be used as guinea pigs. The government soldiers and marines who brought them to their torturous fates also resided on the island.
When the disaster happened, the surviving researchers and the government soldiers all escaped the island but the prisoners were left behind for dead because of the government's perception of pirates as worthless. Those that did not die were paralyzed from the waist down. However, not all prisoners were effected as some still retain mobility in their lower bodies. The artificial dragons survived the disaster without any noticeable harm. Caesar Clown returned to the island after escaping the government prison, where he created various balloon powered contraptions for the prisoners to allow them to regain some semblance of their former abilities and convinced them to serve him. Those prisoners, crippled in a poisonous wasteland and lost all hope saw him as a saint and were blindly devoted to serving him calling him "Master" or "M" which Caesar exploited for his agenda. Their blind worship made them follow every order Caesar Clown gives to them, even when said orders endangers the lives of their comrades.
With the arrival of Trafalgar Law, the prisoners were given new animal legs to replace their damaged legs and became centaurs and satyrs. They served Caesar Clown in two branches, the patrol division who scout and attack any intruders on the island and the hazmat division who subdue intruders using various gases created by Caesar like poison gas and sleeping gas. The hazmat division were also responsible for kidnapping the children brought to the island. Though each division were comprised of centaurs and satyrs respectively, they can be mixed depending on the skills of the members.
Smiley, a gigantic blob of poison was created by Caesar Clown when he collected, compressed and "fed" a Devil Fruit to the gas making it sentient. Because of its destructive nature, he kept it confined in the burning lands. With the Straw Hats and G-5 marines invading his Lab he ordered the creature's release and later sacrificed his pet just to impress the brokers who were watching the incident via video feed.
Brownbeard, was the former leader of the centaur patrol unit and a former New World Pirate. He used to serve Caesar in return for saving his life when he arrived on the island, but when he saw first hand the true extent of Caesar's kindness (ordering him terminated for being captured) he defected and aided the Straw Hats on the island.
A large number of children were held and taken care of in the research facility who were all kidnapped from their home islands and lied to about being ill. These children were secretly used in Caesar Clown's giant research and were tricked into taking a drug whose addictive properties prevent the children from leaving.