From 28 mins (you do have to register to watch - last 10 minutes is the Mendip starfish decoy on Blackdown):
https://uktvplay.uktv.co.uk/shows/the-buildings-that-fought-hitler/watch-online/6248467556001

& a chalk railway tunnel in Ramsgate from 12 mins:
https://www.bbc.co.uk/iplayer/episode/m000w7fr/great-british-railway-journeys-series-13-4-deal-to-margate

Back to where we started, but briefly covering arms storage in WW1, mushroom growing in between, WW2 again & music venue since - from 4 mins:
https://www.bbc.co.uk/iplayer/episode/m000wgxd/great-british-railway-journeys-series-13-6-chislehurst-to-kennington