For decades, the prospect of walking along winding, thyme-scented paths on sun-drenched Mediterranean islands has attracted Brits and other people from Europe's cold north.
But rising temperatures due to global warming are making large parts of southern Europe virtually inaccessible to hikers during the hottest summer months, experts say.
The dangers of extreme temperatures have been vividly illustrated this month with the deaths of several hikers, most of them in Greece.
Age turned out to be an important factor: most were in their sixties or seventies.
Many adventure tour operators no longer offer walking holidays in Spain, Portugal and Greece in July and August due to the high temperatures, which can be especially dangerous for the elderly.
Travel companies are having to adapt to the rapidly changing climate conditions. They are offering more trips in spring and autumn and are focusing on cooler northern destinations such as Scotland and Scandinavia.
"We have made some important changes to our walking offer in Southern Europe. We no longer offer walks in July and August in Portugal, Spain and Greece.
"It has happened in recent years and is related to rising temperatures. The heat was a hazard," said Hazel McGuire, general manager of Europe at Intrepid Travel.
"Scientific studies consistently show that adults over 65 years of age, people with cardiopulmonary and other chronic diseases, and very young children are particularly vulnerable to the effects of heat," noted The Lancet, a British medical journal, in a recent report.
Michael Mosley
The most high-profile case was that of Michael Mosley, the 67-year-old British doctor and health journalist known to millions of television viewers for his documentaries.
He died after walking alone on the Aegean island of Symi in temperatures reaching 38 degrees Celsius - and his death was just one of many.
On Friday, a 70-year-old British man was found dead in the Spanish Pyrenees, four days after he started a hike.
A 74-year-old Dutch hiker was found dead on the island of Samos and earlier this week a 67-year-old German hiker died while hiking near the Tripiti Gorge on Crete's rugged southern coast. He had contacted his wife to say he was lost and out of water.
A 55-year-old American tourist died on the small island of Mathraki near Corfu. Another American, Albert Calibet, a 59-year-old retired police officer, went missing while hiking on the Aegean island of Amorgos and has still not been found.
Mr Calibet had set out via a well-marked path from the north of the island to a small port called Katapola. He knew the island well and was an experienced hiker, making his disappearance a mystery.
"Maybe he chose to take a more difficult path and may have overestimated his abilities. The heat was intense," said Calliope Despotidi, the deputy mayor of Amorgos.
Constantina Dimoglidou, a spokeswoman for the Greek police, said hikers getting into trouble is not new - it happens every year. "But this year, more people seem to have become disoriented during the heat wave."
Athens reaches temperatures above 43C
Greece recorded its first recorded heatwave last week, forcing the closure of the Acropolis and some schools as temperatures in Athens rose to 43C (109F). It is on track to be the warmest June on record in Greece.
Experts warn that walking in countries like Greece during the hottest months is simply no longer advisable.
Intrepid Travel, which offers trips to destinations around the world from Europe to Africa and the Himalayas, recorded 121 more climate-related incidents last year than in 2022, including extreme heat, floods and forest fires.
"Climate change is having a meaningful impact on travel routes. We are seeing a trend towards Scandinavia and cooler climates further north in Europe," said Ms McGuire.
Shoulder season
Intrepid saw a 61 percent increase in mid-season bookings (the period between high and low season) in Western Europe last year and a 29 percent increase to Southern Europe.
The company has added more holiday packages to destinations such as Italy, Spain, France and Portugal for this period, so customers can take advantage of cooler weather.
"Customers want to travel more in the spring and fall and part of that has to do with the heat," McGuire said.
The scorching heat is becoming an increasing problem in Europe as temperatures on the continent rise about twice as fast as the global average, according to the World Meteorological Organization and the EU's climate agency Copernicus.
In Europe, the number of deaths due to hot weather has increased by a third over the past 20 years.
Greece has set up a heat-related health warning system called Heat-Alarm. Scientists who launched it last year said that "the eastern Mediterranean will experience an increase in intense and prolonged heat waves. Future climate projections indicate that such extremes will be the norm for eastern Mediterranean countries over the course of the 21st century."
Older people are more sensitive
Older people store more heat in their bodies than younger people and are therefore more susceptible to heat exhaustion and heat stroke, says Christos Giannaros, one of the scientists leading the project.
Travel patterns in Europe are changing dramatically, says Ginny Lunn, the owner of walking tour company WalkingWomen.
"Our busiest time now is April, before it gets too hot in places like Greece and southern Spain, and then late September, October and November. We are now going to southern Spain in December, where you still have beautiful blue skies.
"In the summer we go north to Norway, which has become very popular, and Scotland. These are now our biggest destinations for summer walking. The heat comes earlier. You just have to rethink how you plan your holiday."
Most of WalkingWomen's clients are over 50 and should be especially aware of the dangers that come with the heat.
"We advise clients to take two litres of water, wear a hat and choose shady routes over the water if possible. We use local guides with a lot of experience so they can adapt to changing weather conditions," says Ms Lunn.
School holidays
While empty nesters and retirees can avoid the months of July and August and instead take vacations in the spring or fall, families with school-age children are bound by the school holidays.
For them, the advice is to change destination - to avoid the hottest parts of Southern Europe in summer and opt for cooler places. Last year, research from InsureandGo, a travel insurance company, found that 71 percent of Britons think Mediterranean holiday destinations such as Spain, Greece, Cyprus and Turkey will be too hot to visit within the next five years.
"We've always tried to encourage our customers to go out of season, but the climate has put more emphasis on that. Why go to Lisbon in August if you're going to be too hot?" says Justin Wateridge, managing director of Steppes Travel, a company that organises luxury holidays around the world, from spotting snow leopards in India to tracking wolves in the Italian Apennines.
"It's about being smart"
"If a customer calls and says he wants to climb Toubkal [the highest peak in Morocco] in July, we would recommend going at another time when it is less hot. Ground suppliers definitely offer more availability during shoulder seasons like spring and fall. It's all about being smart about destinations."
An EU report last year on the impact of climate change on tourism found that 'coastal areas in northern Europe are expected to record significant increases in demand during the summer and early autumn months, while... southern coastal areas will see a significant decline in summer tourist flows.
"Tourism demand is expected to increase in the spring and fall seasons."
Avoiding the increasingly unbearable heat of southern Europe in high summer is not just a matter of safety. "Walking when it's 40 degrees Celsius isn't much fun," says Ms McGuire. "We have to take people's enjoyment into account."
