When adventurers travel to other planes of existence, they undertake a legendary journey in which they might face supernatural guardians and undergo many ordeals. The nature of that journey and the trials along the way depend in part on the means of travel, such as magical portals or spells.
A portal is a stationary, interplanar connection that links a specific location on one plane of existence to a specific location on another. Some portals function like doorways, appearing as a clear window or a fog-shrouded passage, and interplanar travel is as simple as moving through the portal. Other portals are locations—circles of standing stones, soaring towers, sailing ships, or even whole towns—that exist on multiple planes at once or flicker from one plane to another. Some are vortices, joining an Elemental Plane with a very similar location on the Material Plane, such as a swirling pool of magma in the heart of a volcano (leading to the Plane of Fire) or a maelstrom in the depths of the ocean (leading to the Plane of Water).
Passing through a planar portal can be the simplest way to travel from the Material Plane to a desired location on another plane. Often, though, a portal presents an adventure in itself.
First, the adventurers must find a portal that leads where they want to go. Most portals exist in distant locations, and a portal’s location often has thematic similarities to the plane it leads to. For example, a portal to Mount Celestia might be located on a mountain peak.
Second, portals often have guardians charged with ensuring that certain creatures don’t pass through. A portal’s guardian is typically a powerful magical creature, such as a djinni, a sphinx, a titan, or an inhabitant of the portal’s destination plane.
Finally, most portals aren’t open all the time, but open only in particular situations or when a certain requirement is met. A portal can have any requirement, but the following are the most common:
Command. The portal functions only if a particular command is given. A command is usually a word that can be invoked in any language (including a signed language). Sometimes the command must be given as a character passes through the portal (which is otherwise a mundane doorway, window, or similar opening). Other portals open when the command is given within 15 feet of themselves, and they remain open for 1d12 minutes.
Key Item. The portal functions if the traveler carries a particular object; the item acts much like a key to a door. This item can be a common object or a particular one created for that portal. The city of Sigil above the Outlands is known as the City of Doors because it features an overwhelming number of such item-keyed portals.
Random. The portal functions for a random period, then shuts down for a similarly random duration. Typically, such a portal allows 1d6 + 6 travelers to pass through, then closes for 1d6 days.
Situation. The portal functions only if a particular condition is met. A situation-keyed portal might open on a clear night, when it rains, or when a certain spell is cast in its vicinity.
Time. The portal functions only at particular times on the Material Plane: during a full moon, during the spring equinox or winter solstice, or when the stars are in certain positions. Once it opens, such a portal remains open for a limited time, such as for 3 days following the full moon, for 1 hour, or for 10 minutes.
Learning and meeting a portal’s requirements can draw characters into further adventures as they chase down a key item, scour old libraries for commands, or consult sages to find the right time to visit the portal.
A number of spells allow direct or indirect access to different planes of existence. Gate and Plane Shift can directly transport adventurers to any other plane, with different degrees of precision. Etherealness allows adventurers to enter the Ethereal Plane. And Astral Projection lets adventurers project themselves into the Astral Plane and from there travel to the Outer Planes.
Described in the sections that follow are four planar features that connect multiple Outer Planes:
Other planar crossings might exist in your campaign, or it might be possible to walk (or journey aboard a wondrous train or similar vehicle) from one plane to another in your cosmology.
The Infinite Staircase is an extradimensional staircase that connects the planes. An entrance to the Infinite Staircase usually appears as a nondescript door. Beyond the portal lies a small landing with a stairway leading up and down. The Infinite Staircase changes appearance as it climbs and descends, going from simple stairs of wood or stone to a chaotic jumble of stairs hanging in radiant space, where no two steps share the same gravitational orientation. It includes ramps, hovering platforms, and clockwork conveyor belts along its endless construction. The adventure anthology Quests from the Infinite Staircase provides more details about this planar pathway.
The staircase is home to Nafas, a noble genie created by the planar winds that blow into the expanse through its myriad doors. A distant and benevolent observer, Nafas hears wishes spoken throughout the multiverse—wishes he fulfills with the help of adventurers who happen upon his aeolian palace.
Doors to the Infinite Staircase are often tucked away in dusty, half-forgotten places that no one frequents or pays any attention to. On any given plane, multiple doors might lead to the Infinite Staircase, though entrances aren’t common knowledge and are occasionally guarded by devas, sphinxes, yugoloths, and other powerful monsters.
The water of the Oceanus is sweet and fragrant, as befits its headwaters in the Blessed Fields of Elysium. This plane-spanning waterway provides a path through some of the Upper Planes. It flows through each of Elysium’s layers, passes through the top layer of the Beastlands, streams across the top layer of Arborea, and finally drains away somewhere in Arborea’s second layer.
Though it isn’t as far-reaching as the Styx, the Oceanus is still a commonly used path between planes and layers. Trading vessels sail up and down its length, and small towns line its banks. Travelers can usually find a boat to hire somewhere along its shores.
The River Styx bubbles with grease, foul flotsam, and the putrid remains of battles along its banks. The ill effects of the Styx are described under “Hazards” in chapter 3.
The Styx churns through the top layers of Acheron, the Nine Hells, Gehenna, Hades, Carceri, the Abyss, and Pandemonium. Tributaries of the Styx snake through lower layers of these planes. For example, a tendril of the Styx winds through every layer of the Nine Hells, allowing passage from one layer of that plane to the next.
Sinister ferries float on the waters of the Styx, crewed by pilots skilled in negotiating the unpredictable currents and eddies of the river. For a price, these pilots carry passengers from plane to plane. Some pilots are Fiends, while others are the souls of dead creatures from the Material Plane.
The World Tree, Yggdrasil, is a cosmic ash tree that spans the Outer Planes and links them to many worlds of the Material Plane. Its roots stretch into the Lower Planes, touching Hades, Pandemonium, and possibly other Lower Planes. Most of its massive trunk rises through the plane of Ysgard, and its branches stretch through the Upper Planes and across the Astral to the Material Plane.
Some legends describe a great tree, a seedling of Yggdrasil, that the god Corellon planted and tended on the First World at the dawn of time. When the First World was destroyed, seeds from this tree scattered into the void and took root to form the worlds of the Material Plane. Thus, many philosophers and naturalists view all trees or even all plants as descendants of Yggdrasil, part of a vast network of plant life across the multiverse.
Planar travelers can climb among the roots and branches of Yggdrasil to travel from plane to plane or world to world. Some creatures position themselves as expert guides to this vast cosmic network of branching pathways, constantly studying the ever-changing paths as the tree continues its eternal growth.