Drowner’s Map is the second map you usually find after Vidlak Bandit’s Map in Kingdom Come Deliverance 2. Thankfully, compared to other maps this one is easier to solve.
The solution to Drowner’s Map is simple after you pick it up from a submerged treasure hunter when you loot his body. Once you have the map, you need to figure out the location, solve the map, and get the treasure.
Drowner’s Map Treasure Location

This map is very misleading—it shows the treasure sitting on a hill, but it’s actually in a lake.
The drowner’s stash is located on the southern shore of Rocktower Pond, the large body of water to the west of the map where you first made camp in the prologue.

The location is marked as the Water Goblin’s Treasure. Although it appears on the map, the most direct way is to go west from Zhelejov, following the way that passes Bozhena’s shack across the shore.
Follow the river south until it opens up into the pond area, littered with islands and dense beds of reeds.
Look for the Washed-up Chest in the reeds — a wooden chest waiting to be opened. Unlock it with the poachers’ key and claim your haul: 300 Groschen, a very valuable golden crucifix and some silver plates and bowls.
When the path ends, you’ll dismount and wade through the reeds. Stay near to shore, and you’ll soon spy a tiny clay pot to your left, just like the one on the Drowner’s Map.
Inside is also 125 Groschen — not exactly a fortune given the effort involved, but every coin counts in the early game.
If you’d like to visit the water goblin’s lair itself, the Water Goblin’s Hut is further along across Rocktower Pond.