Urban planning wise: I think ivy walls, or other greenery covering residential buildings.
For reference, you might want to look up Bosco Verticale in Italy, or lush green roofs in Norway.
I know this isn’t a catch-all solution, but it could help mitigate climate crisis impact in addition to other options people offered here.
That’s unfortunate, yet not a separate issue from animal farming. They are interconnected, and we can’t fix one without fixing the other.
To get to the point where society pressures ruling class to ban airplanes despite best lobbying efforts, we need to shift the Overton window.
Right now, the Overton window is rather conservative, with most people considering any climate action that requires slightest drop in quality of life completely unacceptable.
Every successful radical climate action, including veganism, helps normalize idea of nature preservation over convenience in public consciousness, so movement can eventually take on more entrenched capital protected interests like jets.
Building anything underground is extremely expensive and energy intensive, as you have to constantly pump ground water and pour concrete to keep walls from breaking under pressure of tons of soil.
So yeah, underground could work, but better used sparingly when benefit outweighs the costs, like maybe in areas that could go literally uninhabitable on the surface. Otherwise not worth it.