When you reach Grozny Grad, the ideal path to follow can be difficult to understand, especially if you are going for Foxhound rank, which requires a speedrun, or if you want to collect every item for a completionist run. The following route minimizes your run time while still covering all areas.
When you arrive in Groznyj Grad Southwest, immediately after The Fury battle, move north along the east wall and enter the northeast gate to reach Groznyj Grad Southeast.
From there, walk to the vehicle and use it as cover while moving to the north side of the area. This allows you to enter in Groznyj Grad Northeast.
If you are doing a completionist run, walk toward the southwest corner of this to area and crawl under the pipes to reach Groznyj Grad Northwest. From there re-enter Groznyj Grad Northeast through the southeast wall.
If you are doing a Foxhound speedrun, skip this step entirely.
In both cases, from Groznyj Grad Northeast, move to the central north part of the area and enter Groznyj Grad Weapons Lab East Wing.
Once you are captured and the torture sequence ends, escape from the cell by calling the radio frequency 144.75 when the soldier walks past the door. Run to the west exit of the area to return to Groznyj Grad Southeast.
From there go straight to the west wall in front of you to re-enter Groznyj Grad Northeast. Walk toward the southwest corner of the area to reach Groznyj Grad Northwest.
Proceed to the far exit of this macro-area and you will finally be out of this labyrinth
Quick version: MGS Delta Groznyj Grad Stealth Path: The Fastest Route