Finally, after many years of wanting to, I went through the Rotherhithe tunnel under the Thames, on foot. It is a vehicular tunnel but bikes and pedestrians are allowed; only about 20 brave souls use it daily, apparently.
Despite a bit of a petrol smell it wasn’t nearly as bad as I had thought it would be [‘really’ narrow pavement, choking fumes, coughing up black tar afterwards]. It was only 7 am though. I saw two cyclists coming the other way. Shame the pedestrian stairs have been closed for 70 years though as it would make the trip much shorter. I guess I must have given the motorists something to gawp at? They can’t see too many runners?