From Dark and Darker Wiki
There are two different types of portals in the game, one allowing you to escape and the takes you down one level deeper.
How to Use
Locate the portal and initiate its activation by pressing the F key. Once activated, a blue/red circle will materialize, and the transfer process will commence as soon as you step into it. It's crucial to exercise caution and be mindful of your surroundings, as any disruptions or enemy attacks while entering the portal could result in a failed escape.
Escape Portal
Escape Portals will appear isolated and only allow a single person out of the dungeon.
Opening a escape portal gives 2 Experience
Opening a escape portal gives 2 Experience
Down Portal
Down Portals will appear in a set three, allowing 3 players to descend together, each of these portals also only allows one player to escape at a time. "When you use the dungeon portal to go down to the lower floors, you will face stronger enemies than the ones found on the normal dungeons."
Opening a down portal gives 2 Experience
You can Teleport to
If you play HighRoll
Portal Spawn Times
You can check the spawn times of portals for individual dungeons: