[mahkeiro]

You could use this kind of technology to extract the heat: https://enerdrape.com/en/solution/

[jodrellblank]

From their FAQ:

> WILL THIS GEOTHERMAL PANEL SYSTEM COOL MY UNDERGROUND SPACE?

> No, the Enerdrape system primarily draws its energy from the ground. This does not affect the comfort of people using the underground space.

[ted_dunning]

Have you seen how small the clearances involved are? The trains are very close to the walls of the tunnels.

[saagarjha]

Definitely an unfortunate domain name they've got there.