I was in London on Wednesday and had the truly awful experience on being on the Underground network on an extremely warm day.
I really don't think it is an ideal place to be if you are over about 40. Well perhaps on a quiet day if there is such a thing. One train in particular I felt was dangerous due to the overcrowding. Perhaps it's always like that but I thought they restricted access to platforms during really busy periods.
49,000 migrants invade Spanish enclave in 24 hours
Locked room for breakables when grandkids stay?


Although having travelled on the New York subway that takes some beating in the filthy stakes, even worse than the London tube if that's at all possible.