Your definition of “safely” probably doesn’t match, but I’ve been enjoying Geowizard’s attempt to cross greater London without walking alongside a road or canal: https://www.youtube.com/watch?v=4476uSeTsg8
The takeaway for me is how much parkland there actually is.
London is famously technically a forest. Though for all towns and cities in the UK there is gigantic difference in the leafiness of the "nice" bits and the normal-people bits.
Which is a shame because trees are a huge uplift to pretty much every measure of urban goodness except for long-term pavement maintenance costs.
The takeaway for me is how much parkland there actually is.