Gorgeous abandoned underground tunnels.pic.twitter.com/hyaWlQYx0F
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Gorgeous! And the poster left from when these pedestrian tunnels closed in the 1960s. This is in Euston Station.pic.twitter.com/0wfUstNPG2
You too can do this.
Book tickets to go into these and similar places! https://www.ltmuseum.co.uk/whats-on/hidden-london …
The booking office shown in a photo above (spot the in and out tiles) is the one in this map in pink and it is on the unused footpath I walked down. These train lines (C&SLR and CCE&HR) in black are now known as the two branches of the Northern line.pic.twitter.com/MmQRR015xH
And the answer to the top tweet is: behind/inside the ventilation shaft on the Victoria line platforms at Euston station. 
Hey! Where is that and what are you doing up there??!!
It's an amazing tour. You should book one! https://www.ltmuseum.co.uk/whats-on/hidden-london …
I will! :D
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