Gotham Gotham Season 5 Episode 5 - "Pena Dura"

[Arachnerd]

That's what I assume, though it isn't exactly the Bat-Cave yet.

Not to mention Jeremiah was more preoccupied with his plan at the time than Thomas Wayne's secret room.

 

[Binker]

Even so, if one person a cavern, if they go back to it years later, they'll see how this cavern has Batman's car, Batman's suit, that means this place is Batman's place!

 

[Arachnerd]

Wouldn't be the first time Joker discovered Bruce Wayne is Batman.