The Dungeon

The Dungeon (地下迷宮) was created using Ramiris' Intrinsic Skill, Small World. The dungeon is a part of Tempest as well as Ramiris' territory. When Rimuru gave Ramiris permission to establish the dungeon, he also granted her extraterritorial rights on that place. The inside of the dungeon is under both Rimuru's and Ramiris' control, established as a special area under the administration of joint sovereignty. Veldora is the final boss and rules over the dungeon while Ramiris supervises it.

Features
The dungeon was created via a number of blocks, allowing the layout to be changed every few days. The environment in the dungeon is fully under Ramiris' control—the sky is visible in certain floors, and it is even possible to make it rain.

While in the dungeon, Veldora constantly flaunts his aura in the 100th floor. Once the magicule concentration increases, monsters will naturally spawn. As it trickles upwards, the upper floors are occupied by small fry with strong beings further in.

The entry fee of the dungeon is three silver coins. Several exclusive magical items crafted by Ramiris are sold at the entrance to aid the challengers' quest:


 * Resurrection Bracelet (復活の腕輪): By wearing the bracelet, any death that occurs in the dungeon will be negated, and the user will be returned to the surface with all wounds healed. It will nullify the pain of fatal wounds and activate ten seconds after death has been confirmed, allowing other party members to revive the fallen. It's given for free for the first time, and costs two silver coins for subsequent purchases.
 * Return Whistle (帰還の): Single-use item that return the user to the outside instantly. In essence, it was an item made for emergency usage. It costs 30 silver coins each and is limited to a single-person.
 * Recording Crystal (事象の記録玉): Allows the user to create a one-time save point and return to the recorded spot during their next entry. It costs one gold coin each.

Treasure chests could also be found within the dungeon, some of which guarded by monsters. There's a chance to obtain Potions, items, coins or prototype Equipment made in Kurobe's workshop. There are three type of treasure chests in ascending rarity and quality: bronze, silver and gold. Bronze chests could be traps or mimics, whereas it is possible to obtain Rare or Unique grade equipment in silver and gold chests, with gold chests having higher chances.

By having newly born monsters swallow items and equipment, it became possible to get item drops from monsters. This incentivized the challengers to hunt more monsters, which also helped in supplying more magic crystals and monster parts in the market.

Floor Notes
Every 10 floors there is a 'Boss Floor' with a 'Guardian' as its boss. There are located just before the boss door that allow an individual to leave the dungeon and return to the lower floors without having to re-do the entire dungeon. Initially, a safe, monster-free zone, was placed every five floors to allow adventurers to rest. It was later scrapped and in its place are doorways at the staircase to each level that allow limited access to floor 95. There, they will be able to sell their loot and access luxuries such as food, beds, and toilets at an extreme premium.

1
The first floor is a square-shaped room spanning 250m on each side. It contains the front desk for managing entries into the dungeon as well as a gym and training areas for learning the basics of dungeon crawling. People who die on this floor, for the sake of safety, are automatically ressurected even without a revival bracelet.

2-4
This is where the dungeon really begins. There are no "Instant Death" traps and the enemies are small fry of F Rank. Treasure Rooms here are guarded by a single D-ranked monster and contain common but useful goods such as low-potions.

5
A floor where tougher monsters of D-Rank can start to be found as random enemies. Treasure Chests start containing actual equipment and sellable market goods starting on this floor.

10
The first floor containing a 'boss' in the form of a B-Rank Black Spider. The first five parties to clear it in a given month will recieve three gold coins.

20
A boss floor containing a B-plus Evil Centipede. The first five parties to clear it in a given month will recieve five gold coins.

30
A boss floor containing a B-plus Ogre Lord and his five subordinates. The first five parties to clear it in a given month will recieve ten gold coins. Additionally "Slotted" weapons will begin appearing as super-rare loot in treasure chests.

40
A boss floor containing the A-minus ranked Tempest Serpent. The first five parties to clear it in a month will recieve twenty gold coins. Additionally "Slotted" weapons will begin to appear as boss drops after this floor.

41-49
At this point the traps begin to get 'serious', one careless step or sharpy turned corner could result in instant death.

49
The primary obstacle of this floor is Slimes. The slimes can merge together creating massive walls immune to physical attacks that prevent escape while closing in on their victims. Other dangers include corridors where the floor is made of slime, slimes that rain down from the ceiling, and insanely durable golems made of slimes. Each of these slimes are extremely corrosive and will completely dissolve a challengers equipment over time.

50
A boss floor jointly guarded in shifts by the A-plus ranked Gozul, and Mezul. The first party to clear it in a month will recieve one-hundred gold coins. The boss chest for this floor has a chance to contain pieces from the unique grade "Minos" equipment set. Additionally "Slotted" weapons will begin to appear as rare drops from monsters.

51-60
These floors are filled with traps made of scientific weapons like laser beams, sonic cannons, poisonous gas, and large numbers of golems.

60
A boss floor that has a Demon Colossus piloted by Gadra as its guardian. After this point the enemies have a much greater intelligence and work in a semi-organized manner, increasing the difficulty drastically.

61-70
Floors filled with Undead summoned by Adalman. These floors are collectively called the 'Haven of the Dead'.

70
A boss floor styled like a necropolis named Deathtopia (死の王国). Its guardian is Adalman with Albert serving as his vanguard and Venti as the tank.

71-80
These floors are occupied by giant insects, including deadly Army Wasps under Apito's command.

79
A floor that has Apito as its boss.

80
A boss floor with the overwhelmingly powerful Zegion as its guardian.

81-90
These floors are a paradise for magic beasts. From the 82nd floor onwards, each floor is guarded by one of the Eight Legions.

90
A boss floor that rarely sees any challengers. Kumara is its guardian and she resides within a luxuious mansion on the floor itself.

91-94
These floors serve as production and storage facilities.


 * 91st floor: Storage facilities for metal ores.
 * 92nd floor: Magisteel production.
 * 93rd floor: A farm to cultivate Hipokute Herbs for potions.
 * 94th floor: Garden and honey production facilities.

95
The 95th floor was established as the residence of the Treants and Elves, thus it became a floor of overgrown greeneries. This dome-shaped floor has the widest area, spanning the diameter of 5 km. Around the door that leads to the 96th floor is the last save point before the final boss. Many important facilities are housed in this floor, including:


 * Adventurer's Inn: Offers food, accommodation, baths and laundry services for prices higher than on the surface.
 * Equipment Shop: Offers special weapons and armors in their storefront, which can only be found and purchased here. Adventurers could also pay to repair their gear.
 * Elf Cabaret: One that's similar to Night Butterflies in the Armed Nation of Dwargon. Only important members with a VIP pass may access this facility.
 * Research Facility: A joint research facility for Elves, Dwarves, Humans and Vampires. The Magic Train was developed here.

There's a door that leads to the 95th floor besides the stairs on each floor, with the entry fee being three silver coins. Those visiting through the door could only access the inn and equipment shop, however. Only those who legitimately reached cleared the 90th floor could have free access to all facilities.

96-99
The dragon floors are inhabited by Dragon Lords that have changed the surrondings to match their element. The floors are arranged in order of strength, fire > ice > wind > earth. The dragons feed on the magicules released by Veldora, hence they can live there without issue.

96
The 96th floor is the Floor of Tremor, as to ridicule the ones that have managed to come this far, a fiendish earthquake will befall them. This floor is guarded by the Earth Dragon Lord Boreas and is filled with constant earthquakes and gravity traps.

97
The 97th floor is the Floor of Hurling Winds, with the threat of lightning striking from the sky. Whether one can break through this floor or not depends mostly on luck. This floor is guarded by the Wind Dragon Lord Notos.

98
The 98th floor is the Floor of Blizzard Hell. If someone stops, they could die; although one might be able to make it through with cold-resistant equipment. This floor is guarded by the Ice Dragon Lord Zephyrus.

99
The 99th floor is the Floor of Inferno, the gateway towards the final boss covered in scorching flame. Heat-resistant equipment is needed. This floor is guarded by the Fire Dragon Lord Euros.

100
On the 100th floor lies an entrance leading to the Dwelling of Spirits, with Veldora as the strongest guardian to protect this gate. Veldora's chamber is a square room 100m wide on each side, and was created in a way that it can be expanded if it's ever necessary. Other than Veldora's Chamber, there are several other facilities, namely:

Veldora's Private Room
A room for Veldora to relax in his human form. It is fully furnished, including a bed. Veldora usually reads his manga in this room.

Rimuru's Private Lab
The place where Rimuru runs his passion projects. He prepared the 1000 Bone Golem bodies for the Daemons recruited by Diablo here.

Ramiris' Private Lab
This is where Ramiris runs her research projects. She was later joined by Dino, and subsequently Shinji Tanimura, Mark Lauren, Shin Ryusei, Lucius and Raymond.

Strategic Military Control Battle Command Center
Commonly known as the "Control Room". This room houses the displays of Physics Magic "Argos" for surveillance, and is the place where military strategy meetings were held. It's possible to directly access other important facilities housed in the dungeon from here.

101
The 101st floor is a temporary floor created and maintained by using Veldora's magicules as fuel to supply Small World. In emergency situations, such as an invasion by a foreign power, the entirety of Rimuru City and its citizens is transported here to avoid destruction and to protect civilians. This massively boost Tempest's protection by forcing invaders to enter the dungeon.

Traps

 * Airtight Room: If one suddenly enters into a room without air, they'll fall from not being able to breathe, at worst die. It is recommended to use wind magic for ventilation.
 * Poison Arrows: Arrows smeared with poison come flying out of nowhere.
 * Poison Swamp: A swamp that is really poisonous. If someone falls into one, they'll get poisoned for sure.
 * Rotating Tile: Drive one's sense of direction mad.
 * Moving Tile: A floor that moves all by its own.
 * Cutting Thread: If one passes by it without realizing, their head will come off. Combined with moving tiles for brutal results.
 * Pitfall: Rather than the damage dealt by falling down, what's awaiting one when they fall is scarier.
 * False Treasure Box (Mimic): A false treasure box that is actually a monster.
 * Slime Pool: A rubbery corridor that swallows its victim half-way across.
 * Slime Rain: Slimes that rain down from the ceiling and dissolve whatever they land on.
 * Slime Doll: A doll made of slime that appears as a regular monster at first. It's immune to most physical attacks and will dissolve the opponents weapon on contact.
 * Monster Room
 * Sealing Room
 * Corridor of True Darkness
 * Low Ceilings
 * Terrain Effect Floor

Trivia

 * Hinata Sakaguchi is the only challenger who has ever reached the 100th Floor and challenged Veldora.