Denise Bennetts finds that people are enticed to sit on the ground at Siena’s Piazza del Campo, but want to dash through the space around London’s City Hall

My wonder is actually a public space, the Piazza del Campo in Siena. The red bricks of the square gently curve in a dip towards the town hall, the Palazzo Pubblico. The buildings around it are an ensemble piece: disparate in scale, size and material but forming a wonderful enclosure, which draws attention to the focal point. The square invites people to relax and inhabit it all year round – it’s so accommodating. The scale of the materials and the way the bricks are laid helps to reinforce the dynamics. And in the summer, people literally sit on the ground – most incredible. The Palazzo’s great tower provides shade that people gravitate towards.

My blunder is the area around London’s City Hall, by Tower Bridge. It’s entirely different in nature, partly because the river view means it doesn’t create an enclosure, but mainly for the subliminal messages the space sends: it’s monochromatic and it’s full of set pieces, so it fails to entice people to linger. The relationship it has with City Hall (which I also don’t like) doesn’t make people gravitate towards the latter. We as architects must try to form enclosures that people will actually want to inhabit.