I spent a lot of time to find out that my calculations of stage 2 were wrong. Then I took the wrong side of the creek and because of low temperature I decided that it would be better to walk back and pass over at a bridge than getting wet. 100 steps away from the concrete structure I found - nothing. But I had luck and discovered the marker a few meters away where it was hidden under some frozen leafs.
At nightfall, a second before I wanted to abandon the treasure quest, I found it.
Greetings Agent Smith