Great Western Coffee Shop

Just like New York Grand Central, there's a labyrinth of tunnels beneath the passengers feet but.....

https://news-sky-com.cdn.ampproject.org/v/s/news.sky.com/story/amp/rail-workers-suspended-after-man-cave-found-under-railway-12082010?amp_js_v=a6&amp_gsa=1&usqp=mq331AQFKAGwASA%3D#referrer=https%3A%2F%2Fwww.google.com&amp_tf=From%20%251%24s&ampshare=https%3A%2F%2Fnews.sky.com%2Fstory%2Frail-workers-suspended-after-man-cave-found-under-railway-12082010

There were beneath Charing Cross, which have been turned to commercial use.

Having had the opportunity to go for a look see underneath Temple Meads,it's a right old rabbit warren down there, including a number of wine cellars,goods lifts ,a dumb waiter and a skittle alley,bomb shelter,and an ARP control area to name a few
Also lots of empty tunnels leading right across the site both from north to south and east to west ,it's damp and dark ,has a great deal of Rats droppings and not so much these days, but used to be problems with human waste discharged from trains in the platforms above, it's quite like an iceberg in that most of the buildings are in fact under the surface.

As well as the main BTM basement, under the disused original station is also fascinating.

Hardly Lex Luther in Superman but  looks comfortable.

If ever you're in Glasgow, there's a tour behind the scenes of Central station.  Alas, cancelled at the moment, but their website is at https://www.glasgowcentraltours.co.uk/index.aspx (https://www.glasgowcentraltours.co.uk/index.aspx), with some pictures. I've been on it and I thoroughly recommend it. The tour guide is brilliant.

I gather there were once suggestions to redevelop these tunnels and spaces as part of a general Temple Meads upgrade (a bit like St Pancras?) but that seems to have been quietly forgotten about.

If you want a station with a warren of underground rooms and tunnels try Waterloo its vast and complex.

Much of Paddington's basements and passageways have over the years been trashed, WW2 damage quite a number, and HEX severed / sealed off a large number of others

Sealed off for a baggage system that was used for no time at all before being scrapped!

911 put paid to that