Ten years ago, a beehive on top of an office building would have seemed like an odd idea. Today, it is becoming a common sight. Across major cities, rooftops that once held nothing but air-conditioning units are now home to thousands of honeybees, and the people who look after them insist the trend is about far more than honey.

“Bees are one of the best indicators of how healthy a city really is,” explains Dana Ferreira, who manages twelve hives across three office buildings in the city centre. “If our bees are thriving, it tells us the local plants, parks and gardens are doing well too. If the hives struggle, that’s a warning sign worth paying attention to.”

The appeal for building owners is not purely environmental. Staff wellbeing programmes increasingly include beekeeping workshops, and some companies now serve rooftop honey in their staff canteens as a small but visible sign of sustainability. Critics, however, argue that urban beekeeping can be overstated as an environmental solution. A small number of hives, they point out, cannot replace large-scale habitat protection, and an overcrowded rooftop can even create competition for food among local pollinators.

Even so, demand for beekeeping courses in cities has tripled over the past five years, and most course providers now report long waiting lists. Whatever its overall environmental impact, rooftop beekeeping shows no sign of slowing down.

I arrived in Porto on a Friday evening with nothing planned beyond my hotel booking, which is exactly how I like to travel. My first impression was of colour: buildings painted in faded blues, yellows and pinks stacked up the hillside above the river, with laundry hanging between some of the windows like decorations left over from a party.

On Saturday morning I walked down to the Ribeira district, where the streets are so narrow that neighbours can practically shake hands across the balconies. I had planned to visit the famous Livraria Lello bookshop, but the queue stretched around the block, so I changed my plan and crossed the river instead, to the Vila Nova de Gaia side, where most of the port wine cellars are found. I hadn’t intended to do a wine tour, but a cellar worker persuaded me to join the next available group, and I don’t regret it — the guide’s stories about the wine trade were more interesting than I expected.

By Sunday I was tired but happy, and I still hadn’t set foot inside a single museum, something my sister will never let me forget. Porto, I’ve decided, is a city best explored without a plan.