From Dark and Darker Wiki
Portal Data is currently up to date for: Patch:6.5#Hotfix 56
Curently, there is only one type of portal in the game, Blue Portal, allowing player to escape the dungeaon.
Previously Red Portals existed that allowed players to go 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. Once the portal is fully materialized the escape process will commence when 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
Static Escape Portals appear as a blue glow on the ground, after some time they will emerge from the ground as a set of 3.
You can check Escape Portals Location on the Map.
Escape Portal Icon in game.
Activated Escape Portal in game.