Crossrail involved tunneling under some of the most expensive property in the world, while passing within inches of existing underground tunnels. There are several fascinating documentaries.
Do you remember where to find those documentaries?
Sadly it's no longer on iPlayer in the UK but if you use a bit of search wizardry I'm sure you could find it.
The 15 Billon Pound Railway
https://www.bbc.co.uk/programmes/b04b7h1w