D&D is already full of strange worlds that you can use as the dungeon master or explore as a player. Here are 5 of those strange D&D worlds that you can consider using in one of your D&D games.

1. Sigil, the City of Doors: Featured in the Planescape campaign setting, Sigil is a city located inside a massive torus that floats at the center of the multiverse. The city is connected to every plane of existence through a series of portals, known as doors, making it a melting pot of cultures, races, and beings from across the multiverse. It is ruled by the mysterious and enigmatic Lady of Pain.

2. The Feywild: The Feywild, also known as the Plane of Faerie, is a parallel dimension to the Material Plane. It is a realm of wild magic, vibrant colors, and untamed nature, where time flows differently and emotions are amplified. The Feywild is inhabited by fey creatures like elves, pixies, satyrs, and unicorns, as well as powerful archfey who rule over vast domains. The world is a place of whimsy and wonder, but it can also be dangerous and unpredictable, as the fey often operate by their own rules and capricious natures. The boundary between the Material Plane and the Feywild can be thin, and characters may find themselves accidentally stepping into this strange world, or they may be drawn in by the fey for some specific purpose.

3. The Far Realm: The Far Realm is a bizarre and alien plane of existence, which is completely different from the other planes in the cosmology of the D&D multiverse. It is a place of madness and chaos, inhabited by unspeakable horrors and aberrations. The rules of reality, time, and space do not apply in the Far Realm, making it an incomprehensible and unsettling world.

4. Pandemonium: One of the Outer Planes, Pandemonium is a chaotic and windswept plane of tunnels and caverns carved into solid rock. It is inhabited by madmen, outcasts, and creatures of chaos. The howling winds of Pandemonium drive its inhabitants to insanity, and the twisting tunnels make it easy to get lost. It is a realm of madness, darkness, and unending noise.

5. The Shadowfell: The Shadowfell is a parallel dimension to the Material Plane, often referred to as the Plane of Shadow. It is a dark and twisted reflection of the Material Plane, a world of gloom and decay. The landscape is a bleak and desolate version of the Material world, with colors muted and the sky perpetually overcast. The Shadowfell is inhabited by undead, shadow creatures, and other beings associated with darkness and death. It is a place where negative emotions are magnified, and the atmosphere can be oppressive and disheartening. Despite its sinister nature, the Shadowfell is also a realm of potential and transformation, where lost souls may find redemption or renewal. The boundary between the Material Plane and the Shadowfell can be thin, and characters may find themselves crossing over into this eerie world, whether by accident or by design.

How about we come up with five strange D&D worlds? The Clockwork Realm is one I used in my first 5th Edition Dungeons and Dragons campaign.

1. The Hollowed Earth: In this world, characters find themselves in a vast subterranean realm, where the very core of the planet is a sun-like energy source that illuminates the land below. Giant mushrooms serve as forests, deep underground lakes harbor strange aquatic life, and the entire ecosystem is populated by luminescent creatures that have never seen the surface world. The kingdom is ruled by sentient mole-people, and players must navigate this bizarre underworld to survive.
2. The World of Mirrors: In this world, everything is a reflection of something else. The sky, the ground, the trees, and even the inhabitants are all mirrored reflections of a reality that exists somewhere else. Players can move between the real world and the World of Mirrors through any reflective surface, like a pond or a polished shield. The World of Mirrors contains secrets, treasures, and dangers that mirror those in the real world, but they may be twisted or distorted in unexpected ways. Actions in one world may affect the other, and players must navigate the complexities of both worlds to succeed in their quests.
3. Clockwork Realm: The world is a giant, intricate clockwork machine. The ground is made of spinning gears, and the trees are mechanical contraptions. The inhabitants of this world are humanoid automatons with a semblance of life. Quests could involve repairing broken parts of the realm, discovering the mysterious creator of this clockwork world, and unraveling the secrets of how it all works. Players would have to deal with hazards like gears that suddenly start spinning or belts that can whisk them away to unknown parts of the world.
4. World of Dreams: In this world, reality is shaped by the collective dreams of its inhabitants. The landscape can change in an instant, and the only constant is change itself. Players must navigate through ever-shifting environments, battle surreal creatures from the deepest nightmares, and interact with NPCs that may not be what they seem. The world might have dream towns where people’s wildest fantasies come to life, and nightmare forests that harbor fears incarnate.
5. Reverse World: This world is a topsy-turvy place where everything is backward. The sky is below the characters’ feet, and the ground is above their heads. Gravity works in reverse, causing characters to fall up. Day and night are swapped, with the sun shining at night and the moon during the day. Language is spoken backward, and time flows in reverse. Players must navigate the upside-down world, learn to communicate in reverse, and figure out how to deal with events that unfold in reverse chronological order. They may even encounter their future selves as past events play out.

You can use some or all of these ideas as standalone adventures, or connect travel between these strange D&D worlds as part of a larger quest. There’s no reason not to use a mix of your own made-up worlds alongside D&D’s plethora of already existing strange worlds. Feel free to modify the existing D&D lore to make it your own, but also to keep your players on their toes.