https://store.steampowered.com/app/1141960/Pathologic_2_Marble_Nest/
https://store.steampowered.com/app/505230/Pathologic_2/

https://www.youtube.com/watch?v=cAC2oz6epcQ

Pathologic 2: The Marble Nest DLC, a two-hour spinoff story in the world of the Pathologic 2. Play for a single day as Dr. Daniil Dankovsky, a scientist from the Capital, a fighter of death, and another doctor trying to save the Town alongside the Haruspex, and uncover a different perspective on the events - and Death itself.

The Marble Nest is free for everyone who had the base game in their library before its release. For the rest its $9.99.
The Marble Nest can be launched from the main menu of the Pathologic 2.

Come, little birds, and gather around the marble nest...