I always thought the concept of urban beaches was a bit depressing. I remember back in Birmingham, every Summer a cheap flight company would dump a ton of sand next to a fountain in the middle of one of the squares and call it a 'beach'. But as someone who could happily live in a beach hut with an ice cold coke (in a glass bottle) and a tube of suncream even our little rooftop beach makes me happy.
I used a wooden crate we were using as a veg box and a bucket of sand that my Xmas tree stood up in - just add toys and small children with inherited capacity for small pleasures (and by toys I mean little yellow diggers and mummy's vintage teaspoons!)
And a little flag to make Sand-ringham Castle:
... and after the revolution: