[edent]

Sort of, yes. https://en.wikipedia.org/wiki/BT_Tower#Secrecy

[biofox]

Two more examples of exchanges that were kept secret:

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

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

[lxgr]

Wait, what? What else were people supposed to assume about the purpose of a huge tower with very noticeable horn antennas (widely used for long-distance phone calls over line-of-sight microwave at the time)?

[razakel]

It also had a restaurant open to the public.

[ta1243]

The one place in London you can't see it