[postcynical]

13bln$ gets you a 35 mile tunnel thru the swiss alps.

https://en.m.wikipedia.org/wiki/Gotthard_Base_Tunnel

[yywwbbn]

I’d assume that drilling a tunnel under a mountain would be significantly cheaper than digging one in a densely inhabited city (in a seismically active area).

[postcynical]

3miles for $2bln under densely inhabitated city.

https://en.wikipedia.org/wiki/Weinberg_Tunnel