To complete Okri's Secret Stash Challenge, you need to push 10 hidden switches that are scattered around the Pit district. Follow next images to find them and open the door to the secret stash.

We'll begin in the market area.

Heres the first switch

Right near the first one, you need to jump over a stone wall and then you'll se 2nd switch on the wall left from the arch

go through market area again until you'll see the Pit district. Turn right and cross the bridge
Jump to the balcony and move forward
3rd one is behind this box

Go back like shown on the picture and move forward
The 4th switch will be behind the house that you can move through

continiue moving forward and then turn left to the small alleyway
Behind this tiny box is 5th one

jump down and turn right
move forward and then turn left to go down again
turn left and move to the town wall
turn left again and you'll see a bunch of boxes, the 6th switch is behind them

turn back and follow the way shown on pictures, we need to go down the sewer for 7th switch
go up the stairs and turn left into the small tunnel. In the end of that tunnel you'll see 7th switch near the ceiling

Now you need to back track a little bit. Follow the images
Undet that wooden walkway you'll find 8th switch

Go back to the place where you turned left to the wooden walkway and go futher into the street
Turn right and then left and go up the stairs, you'll find a lot of tents on your right as soon as you'll get upstairs
Climb the ladder
walk on the edge and get to the baclony
Heres the 9th switch, 1 more to go!

Now get down and turn right and then right
Go forward and then turn right, in the corner you'll see a box, climb on him and push 10th switch
Now get back to the stairs that you've been on, when you were going to the 9th switch.
Go down the stairs and turn right and right again
Theres a opened basement right behind this tree, you've done it!

Thanks to the people who helped me completing this guide and helping all Vermintide 2 players.
Thanks to Stirb'orn ( https://steamhost.cn/steamcommunity_com/profiles/76561198015800809 ), Poor F***ing Infantry ( https://steamhost.cn/steamcommunity_com/id/TekDek ), Zany Old Coot ( https://steamhost.cn/steamcommunity_com/id/Zany_Old_Coot ), The Fanciest Feast ( https://steamhost.cn/steamcommunity_com/profiles/76561198130698134 ) for the help