Mysterious Island

Mysterious Island is a tentative name for a deserted island located somewhere in the New World that appears in the Mass for the Dead game.

Background
Two hundred years ago this island was a base of operations for pirates. Their island hideout was however discovered and a battle took place in their hidden port. While they fought the attackers, through intention or accident they broke the mechanism that opened the door to the cave passage.

The pirates attempted to make out to sea with their treasure, but apparently a Giant Mollusk had entered through the waterway and into the small port. In the ensuing chaos, the pirates and attackers were all killed when the monster broke in and destroyed the ship.

Mass for the Dead Arc
In the present, Momonga was conducting an experiment to connect a [Gate] to the Mine Dungeon to deliver resources to the damaged Great Tomb of Nazarick. Momonga sent a Skeleton to test it but discovered that the [Gate] connected to the island instead. While it was a failure, the summon, had found a scroll with a map of the island.

Interested in this find, after Pandora's Actor estimated the artifact to be over a hundred years old, Momonga sent the Pleiades, Slimeko and the game's protagonist to investigate. The maids equipped with swimsuits explored the island, but even though they split up, they were unable to find any clues around the perimeter of the island save. Turning to into the jungle, the maids and their allies discover a well indicating that the island was inhabited.

The team goes to the last place on the island they had not checked, a deep cave near the reefs. Reaching the reef and the cave, Entoma Vasilissa Zeta uses her insects to do a survey, however they reveal to her that something inside the cave is obstructing a passage. Inside the cave, they find it goes deeper then expected, and discover the obstruction. Initially thought to be a wall to turns out to be a Giant Crustacean. After killing the creature, the cave is revealed to go deeper. What they find is a dead end, until they find that the wall is fake. Breaking it down, they find a section of the cave to be filled with undead. Fighting their way through the group come to the ruined remains of a pirate hideout. Finding the leader, a Death Knight, the maids defeat the undead. The pirates' treasure is believed to be in their ship which is submerged in the hidden port. After draining the water, by blocking the waterway and forcing the water to the entrance, the wreck is found. However before they begin their investigation, a Giant Mollusk attacks them. After defeating it the group retrieve the ship's cargo and return to Nazarick.

Layout
An isolated island with a large forest area situated inland. The outer circumference of the island is almost all sandy beaches, except for some reef areas.

Forest
A dense canopy located in the center of the island. A well is also located there, where the former inhabitants drew fresh water. A road once existed, but over the years the grass grew over it, covering the path completely.

Reef


Located away from the sandy beaches, it contains a lot of rocks and the terrain is ideal for creatures like crabs and slimes to hide.

Cave
Along the reef there is a cave-like side hole in the back of a cove. It acts as the inland entrance to a hidden pirate hideout. The pirates developed a crafty method to guard the door to their hideout. Taking advantage that the inland entrance of base the a burrow of a giant crab and the fact that it blocked the entrance during the day, it was the perfect defense. Since it was nocturnal all the pirates had to do was schedule a time of when the crab was out at night and enter. Going deeper were several burrows of smaller crabs where there was a second door leading to the hideout.

Pirate Hideout
The main sanctuary of a crew of pirates. It could be accessed through a cave in a cove on the island. After passing the crab's domain, a second wall hid the main part of the pirate's base. There wall was actually a door which could be activated through a mechanism. On the other side was a hidden pool that connected to the sea and where the pirates had docked their ship.

Known Inhabitants
The island was home to a crew of pirates, but also contained some fauna like crabs and green slimes. Due to the negative emotions of the dead pirates, they eventually became undead such as skeletons, skeleton warriors, and even the leader becoming a Death Knight.

Trivia

 * Based on the logbook of the pirates discovered by the Pleiades, the pirates had stopped at a port town of the Re-Estize Kingdom, indicating that the island may be located in either the sea west to the Kingdom or in the Rhynd Sea at the north.
 * Scenes from the island were later reused by the game developers in a later special event.