New updates to Zombox
The world now features an elaborate, underground sewer system that you can explore by entering/exiting various manholes throughout the city. The sewer system features shops, medic stations, etc, and will eventually be filled with NPCs -- the remaining survivors of the apocalypse -- who you'll be able to interact with.
Here's the overall layout of the 3 main sewers (the largest one is still a work-in-progress):
Here's a .gif showing the player entering a sewer, looking around a bit, and then exiting: