5. Picasso's Guernica.
Sofia Reine, Madrid.

But thinking perhaps the entire Guernica wing of the Sofia Reine would give it the necessary context, so the two armed guards can be there too, I guess.
I should have dropped a suggestion into the box that the gallery should consider installing bench seats, as the aforementioned guards make threatening moves towards those who even think about sitting on the floor in front of this.
And I'd like to thank whoever took this photograph for sensibly ignoring all the 'no photography' rules that the Sofia Reine still anachronistically adheres to.