If you want to unlock the subway system in Stray, you'll need to find the atomic battery. Once you've met Clementine in Midtown and fetched the worker's jacket and hat for Blazer, you'll be able to sneak into the Neco factory. After avoiding the Sentinels, you'll reach the area where the atomic battery is kept, but getting to it is a little tricky...
Read more.
Stray: How to unlock the atomic battery
Source: PC Gamer (opens in a new tab)