From Dark and Darker Wiki
Portal Data is currently up to date for: Patch:6.5#Hotfix 56
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. Once the portal is fully materialized the transfer process will commence as 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
Escape Portals will appear in a random place in the map, allowing a single person out of the dungeon. They can also appear as a set of 3 Escape Portals, allowing one person each.
There are also Static Escape Portals emitting a blue glow when they open that will appear in particular spots on the Map, allowing a single person out of the dungeon.