Ring 5: The Ocean of the Unknown

The Ocean of the Unknown is the fifth ring in Luigi's Towers of Oddity (Fan Idea), it contains Hard-Remorseless towers and Extreme and Terrifying Soul-Crushing Towers, a Remorseless Citadel, and a Challenging Mini Tower. It requires 24 World 1 Tower beaten and contains 17 total towers. The whole lobby is in a glass aquarium at the bottom of the ocean, and the towers are scattered throughout the ring, sunken in the depths of the water. (The water doesn't affect gravity or anything.) The Min Tower is located in a field of coral, the SC Tower is in a huge trench, and the Citadel lies under a huge boat and ascends to the top of the boat. If you follow a staircase in the aquarium you will be led up to an island in the water that is connected to a cave, arriving here will transport you to Ring 4: The Caves of Descension. Additionallly, there is a submarine under the lobby that can be accessed by doing a small obby in the viewing area, hopping in will teleport you to Ring 6: Jungle of Secrets if you've unlocked it.

Starter Towers
Tower of Underwater Chaos (Hard)

Tower of Evil Traversing (Hard)

Tower of Limited Oxygen (Hard)

Skillful Towers
Tower of Extreme Sadness (Difficult)

Tower of Aquatic Mayhem (Difficult)

Tower of Earthly Purposeful Helpfulness (Difficult)

Tower of Hopelessness (Challenging)

Professional Towers
Tower of Evident Demotivation (Challenging)

Tower of Doom (Intense)

Tower of Trolls and Traps (Intense)

Extremely Hard Towers
Tower of Not Looking Down (Remorseless)

Tower of Inner Hatred (Remorseless)

Tower of 20,000 Leagues (Remorseless)

Mini Tower
Mini Tower of Rising Tides (Challenging)

Citadel
Citadel of Ocean Evacuation (Remorseless)

Soul Crushing
Tower of Decreasing Oxygen

MToRT
Go to the lobby's credits area and press a button that is behind a statue of the creator. A platform in the floor will rise revealing MToRT's portal

CoOE
Go to the Extremely Hard Towers section and go to ToIH's portal, corner clip in a corner on the side of the portal and you will be in the portal room.

ToDO
Dance clip into one of the glass aquarium exhibits and squeeze through a 1 stud gap in the wall, the gap will lead to ToDO's portal room.