Portal

Portals are a feature in No Man's Sky and can be found on select planets. They normally appear as an individual portal, with small stone towers on each side of the "entrance." Currently, it is not known how they are activated.

Recent cassette tapes sent by Hello Games seem to allude to these mysterious structures.

Summary

First announced during the 2014 Game Awards, portals have the ability to take the player to a random part of the galaxy. In the pre-release version of the game, the only planets known to have portals were Gorogohl and Yaasrij.

They normally appear as an individual portal, but some have been discovered with multiple smaller portals surrounding a larger one.

Known Portal locations

For a list of known (and often marked portals) see Portal locations.

Function

Pre-release Info

Note that this is pre-release info and does not apply to the currently known features in the post-release build of the game.

These structures act as wormholes; it has been shown that black holes will act in the same way.

If passed through in one direction, a portal will transport you to another planet closer to the center of the galaxy. And while the resources will be more valuable there (especially if brought back to the area of the galaxy where you came from), the dangers will also be increased. To get back to your ship you will need to enter the portal located on the new planet you have been transported to.

How to locate/activate

At Ruins that have flagpoles, the direction of the symbols on the flag poles (circles/spirals, triangles, and hexagons) point to a Portal. There are several theories/rumors regarding the specifics, but the general method is to treat each symbol as a targeting reticule and follow a straight line through the symbol on the pole. Eventually, you will reach a Portal. To date, no one has been able to accomplish activation of a Portal.

Debunked Theories

"There is only one portal per planet/moon." (It has been proven that there can be multiple Portals.)

"Follow the direction that the flag itself points on a flagpole leads to a portal." (Does not necessarily lead to a Portal, although it may indicate wind direction. It may also lead to a Portal by sheer luck/coincidence.)

"Push a golden ball from a (Gek?) Ruins through the opening in a Portal to activate it." (Does not activate a Portal.)

"Collecting all of the Gek, Korvax, and Vy'keen words will activate a Portal." (Collecting these words does not activate a Portal.)

"Achieving '10' score on all Milestones activates a Portal." (Completing the milestones does not activate a Portal).

"Having various combinations of 'collectible' item in your Exosuit inventory activates a Portal." (Does not activate a Portal.)

"The sunlight passing through the Portal at <some specific time-of-day> activates a Portal." (Portals may not always align properly with the sun in the system, so the sunlight may never meet any specific alignment.)
"Planets with no flagpoles do not have portals." (There are a mix of Ruins both with and without flagpoles on some planets, and there are portals on these planets.)
"One particular Monolith will present a doppelganger, and if answered correctly, a new multi-tool will be offered. Accepting the multi-tool will allow a portal to be opened." (The multi-tool does not open a portal, nor does it contain any special technology.)
Collecting all of the Gex, Korvax, Vy'keen AND Atlas words may activate a Portal.

Unverified (but plausible) theories

Activation of Atlas Monoliths turn on the world power grid and the planetary overseer will thank you. Once power grid is operational the monolith will shoot a blue flare on flyover. The other other three alien type monoliths will also shoot the blue flare upon activation. When all 4 type monoliths are activated, the maproom accessible by Atlas level 2 pass at special observatory shows system map. (You are welcome)
All of the Portals found in-game so far may be "Exit" Portals, and no "Entrance" Portals have been found yet. "Entrance" Portals might only be found upon exploration of more advanced Galaxies.

Some combination of word knowledge, Milestone completion, conversations with Polo/Nada, and other in-game activity/achievement may activate a Portal.

Portals may not be enabled yet; they may be enabled in future No Man's Sky updates.

The markings on the Portal may indicate some way of activating it. The markings are roughly representative of the portal itself, but they are (to date) too cryptic to decipher.

Activating a Portal may have something to do with stellar/lunar alignment, and it may have something to do with the time-of-day on the planet.
Which specific symbol to follow on a flagpole (circle, triangle, hexagon) may depend on the dominant alien race (Gek, Korvax, Vy'keen) on the planet. Other symbols may point to other features.
Ruins that have 2 flagpoles may point to portal, whereas Ruins with 1 flagpole may/may not point to other features.

Speculation

It has been hinted through various interviews that the world the player is transported to is important to the overarching story and may be where the bulk of the backstory will be found.

The occurrence of portals at the edge of the galaxy should be extremely rare if none at all, and then start to increase as the player reaches closer to the center of the galaxy. However, for contradictory evidence, see below Gallery: Portals in player's Starting Planet or Starting System.

If you die on the new planet, it is unknown where you will spawn. Possible options include:

by your ship on the old planet
by a default ship on the new planet
by a default ship on a space station orbiting the new planet

The reason that no-one has been able to open/activate a portal... is unclear. All of the portal activation ideas, and every other theme in the game, are conjectural. It is possible that Portals are not able to be activated at this time.