In the Krypt, the following locations will give you secret treasure chests. They each contain 5,000 Koins; there are a total of 4 secret chests to give you an additional 20,000 Koins! Look for small, green areas on the ground that resemble acid moving around in a puddle.

Bloodmarsh
Along the wall, in front of a demon head sculpture.

Deadlands
To the right of DL-52, left of the building.

Hollow of Infestation
Along the wall, in front of a demon head sculpture.

Meadow of Despair
To the right of the Necropolis entry.