Most fantasy worlds include portals. Broadly speaking, they come in 3 varieties: portals to travel somewhere else in the world, two-way bridges to other dimensions or planes and one-way portals used to summon creatures, gods and monsters.
One of the biggest issues with portals, in my opinion, is that they are usually same-y and never quite manage to produce the level of amazement that they should. The characters, upon meeting a portal, are coming to the life-changing realization that interplanar, dimensional or extremely fast travel exists, and this has huge implications. Surely the characters would wonder, who can do this? Is this destroying our world? Would the gods approve? Would I be alive on the other side of it?
And yet the players, who have been reading and playing fantasy, and are accustomed to fast travel in video games, just see that big archway with ondulating energy at the end of the dungeon and think “here it is, a teleportation device”. And that is not so fun. Or maybe they just see the villain create and use one to get away in the nick of time, which should be the real meaning of the phrase “the yawning portal”.
No journey through a portal should be consequence-free. They are, after all, magical reality-bending devices.
Roll 1d12 per column. The portals in this table are mostly evil…
|Dice||Appearance||Consequence on the traveller||Additional twist|
|1||A small pond with fishing rods all around it. Large glowing fish swim in the water and that teleport the person who catches them.||The traveller ages 1d12 (human) years with a 50/50 chance of being older or younger||The portal can only be crossed by multiple creatures at once|
|2||A spiral wooden staircase going down into a thick fog.||The traveller leaves a copy of him or helself behind which becomes a golem controlled by the portal itself.||The portal is known by most through a prophecy, and those who cross it will not go unnoticed.|
|3||A full plate armor suit that one has to get inside of.||The traveller arrives carrying a severely debilitating disease that can be cured by doing the journey in reverse.||The portal appears shattered, broken, or in disuse, but recomposes itself for those who carry a key.|
|4||A prisoner cage floating above the floor. Only those who have the key can travel.||The portal is sentient and reports the journey to its creator, even if the creator is dead.||The portal is part of a network.|
|5||An arrow with fletching made of dozens feathers collected from monsters. Pulling each feather teleports the traveller to a destination (or summons a different monster)||The portal collects a piece of soul of the traveller, stores it, and binds it to the next traveller. Whoever crosses will in turn carry a piece of a soul of a previous traveller, who may have been wicked or cursed, or may just give insights into their thoughts.||Somewhere in a library, there is a log of every person or creature that has travelled through|
|6||A vine crawling up and over a mossy wall.||Travelling through the portal brings an ancient creature back into the world.||Crossing into the portal causes vivid, terrifying nightmares.|
|7||A book chained to a shelf. It has dozens of pages with names of places or monsters written in, one per page. Writing in a new page results in transport.||The traveller acquires a ring on his or her index finger marking his journey through the portal. The ring cannot be removed and is immediately recognizable by others.||An hourglass next to the portal slowly counts down the time until the portal disappears. It started decades or centuries ago.|
|8||A small wooden lifeboat in the middle of the room or on land. Pulling out the oars and rowing results in transport.||The traveller loses eyesight severely, and will only be able to restore his or her sight by committing a murder or another atrocious act.||The portal itself is the familiar of a wizard or someone’s creature. It has allegiance and loyalty.|
|9||A set cobblestones lying on a shelf that needs to be laid down as a road leading into a wall. There are markings on the floor of people having done that before.||The portal imposes a tax on the traveller and an item he or she carries will be shattered during the journey.||The portal seals shut after the journey for 2d20 days.|
|10||A goblet filled with solid red wine, which liquefies immediately after being picked up and portals those who drink it.||The journey through the portal disorients a character permanently, and he or she will no longer remember what home looks like.||Travelling causes strong thunderstorms, sandstorms, or other extreme adverse weather at the destination.|
|11||A sundial that transport whoever stands on the tip of the shadow it casts. No matter what time of the day it is, the shadow always points to noon.||The first journey through the portal teaches the character a spell or a skill. All subsequent journeys curse the traveller for his or her arrogance.||The journey feels instant but takes 1d8 hours in real time.|
|12||A table with an orc corpse that has been stabbed hundreds of times in the chest and yet seems fresh and does not bleed. Pierce through its heart once more.||Travelling through the portal drains spell slots and abilities for twice the normal amount of time (e.g. 2 long rests).||Wild animals and creatures will be able to smell the scent of the portal on the travellers for days and they will be marked as prey.|