Some people on this thread don’t know the meaning of walkable.
A lot of these cities are not walkable because they are big and sprawling.
But you don’t need the whole of a city to be walking distance. For a short break you need two or three good areas to explore near your accommodation.
Obviously the whole of London isn’t walkable but if you stayed at Premier Inn Waterloo, for example, you could do a day exploring down the river, S Bank, HMS Belfast, The Globe, Tate Modern, The Golden Hinde, Borough Market. Another day crossing Westminster Bridge, Houses of Parliament, Westminster Abbey, Downing Street, Etc. Or Hingrrfird Bridge: Trafalgar Sq, St James Park, The Ritz, Royal Academy, or go Covent Garden, China Town, Soho.
Paris , similar opportunities.
Etc.