Enter the partially flooded tunnel and start exploring. Your current destination is the room to the north-east. Search it thoroughly, there are two crates to find. Open the first to get 110 XP, open the other to find a Relic (reward: 25 XP).
Check out the area left of the main entrance and use the torch to ignite some debris; you'll unlock a way into a sideway section. Approach the table to get a new piece of Gear, Pry Axe (reward: 250 XP).