The Monsanto Forest Park in Lisbon is three times the size of Central Park. It’s so big, in fact, that you can get totally lost in it and forget that you are in a capital city. Known as “Lisbon’s lungs”, the park has cycle paths running through the eucalyptus, oak and pine trees and wildlife thrives, from rabbits to owls and bats. The six square miles of trees and greenness have great views over the Portuguese capital and the Rio Tejo, if you need a reminder that you are only a short stroll away from the city centre.

Cities are, quite literally, nourished by their parks. Trees remove pollutants from the air and provide cleaner, cooler air and water. They trap dust, ash, pollen and smoke. They absorb carbon dioxide – studies show that they absorb and store an annual average of 13 pounds of carbon each year while one acre of trees produces enough oxygen for 18 people annually.

Little pockets of urban paradise sustain cities around the world. Villa Borghese in Rome, which was bought from the Borghese family and turned into a public park in 1903, retains much of its noble charm and is an oasis of cool in the sweltering summer months. The Jardin du Luxembourg in Paris is similarly regal, with lush English gardens on one side.

Letná Park, elevated above Prague, has an incredible panorama of the city from the Hanavsky Pavilion. Others are very much city parks. Tiergarten Park in Berlin is bordered by the Brandenburg Gate and Potsdamer Platz, which means you can’t really get lost in it – but equally its proximity to such landmarks stops the city from feeling too oppressive.

London is much greener than you might think. It has 3,000 parks, 30,000 allotments, three million gardens and two National Nature Reserves. Which means that a whopping 47 per cent of London is green space. The famous parks – the eight Royal Parks, including Hyde Park, Regent’s Park and Richmond Park to Greenwich Park – are complemented by hidden gems such as the conservatory in the Barbican and the Islamic Gardens at the Aga Khan Centre.

Every major city in Europe has a “green lung” – a space to breathe clean air and take a moment to appreciate all that nature has to offer.