I went into King's Cross St Pancras Underground station today via the
new(ish) entrace close to KX platforms 9-11. There is an enormous
illuminated Underground roundel above the steps down into the station
- and I wondered if it is the largest roundel on the network, or
whether there are other giants to behold? (I'm not being fussy, you
can play around with this question in different categories of signage
if you like - just one of those Friday afternoon thoughts!)

Cheers,
Sam