To break the hatch in The City of the Sun Quest in Horizon Zero Dawn, head upstairs in the house you are in and then up a ladder to the top floor. There you will find a crate of ingots you can push down on the hatch to break it revealing a secret room. Here's the in game quest tracking for the step shown in this video:
The City of the Sun
Investigate Olin's Apartment
- Find a way to Break the Hatch