He's not in a cave, but he is building it out of scraps. It's "Improvised" in the sense of "Improvised Explosive Device." Tony Stark is well known in Marvel Comics for his high-tech Iron Man suits ...

But there is a deeper meaning behind it. It's a callback to Tony Stark building his first suit in 2008's "Iron Man," which kicked off the entire MCU. One of the main plot points of "Endgame" is ...