They were sitting cross-legged on the ground, palms pressed against a mosaic of black and white tiles set into the concrete. The design was circular, littered with wilting rose petals. Pennies arranged along the inner ring. At its heart, a single word. Imagine. I wanted to get my camera out. Photograph them. But I desperately needed to sit down. I’d seen Soho, the Flatiron Building and half of Central Park before arriving here at John Lennon’s monument, but I’d made a huge mistake. I’d ...