Modern graffiti began in big cities in the United States in the 1970s. In New York, young people wrote their names, or 'tags', in pen on walls around the city.

    One of the first 'taggers' was a teenager called Demetrius. His tag was TAKI 183. He wrote his tag on walls and in stations in New York. He did it just for fun and he had never imagined his behavior would have launched an amazing art campaign. Other teenagers saw Demetrius's tag and started writing their tags too. Soon, there were tags on walls, buses and trains all over New York.

    Then, some teenagers started writing their tags with aerosol paint. Their tags were bigger and more colourful. Aerosol paint graffiti became very popular in the 1970s and 1980s. It appeared on trains, buses and walls around the world.

    In the 1990s and 2000s, a lot of graffiti artists started painting pictures. Some artists' pictures were about politics. Other artists wanted to make cities beautiful and painted big, colorful pictures on city walls.

    In some countries, writing or painting on walls is a crime. Sometimes, graffiti artists have problems with the police. In other countries, artists can draw and paint in certain places. For example, in Taiwan, there are 'graffiti zones' where artists can paint on walls. In São Paulo in Brazil, street artists can paint pictures on walls and houses. Their pictures are colorful and beautiful. Some tourists visit São Paulo just to see the street art!

    In Bristol in the UK, there is a street art festival in August every year. Artists paint all the buildings in a street. Lots of people come to watch the artists and take photos. You can see exhibitions of street art in some galleries too. There have been exhibitions of street art in galleries in Paris, London and Los Angeles.

    Guinness World Records has long been recording some of the most amazing and astonishing travel and tourism facts. Here we are sharing some of the most unbelievable record-breaking accounts, all fully fact-checked and Guinness-approved.

Largest Ice Structure—The Ice Hotel in Sweden

    Each year, the ice hotel in Jukkasjarvi, Sweden, is rebuilt from blocks of frozen ice from the nearby River Torne. Covering an area of 5,500 square metres, the hotel is unsurprisingly open seasonally, from December to March, when it melts away. In 2015, the hotel celebrated its 25^th anniversary, complete with an ice bar, an ice church and ice bedrooms—one even featured a London Tube carriage made entirely of ice.

Tallest Waterfall—Angel Falls, Venezuela

    The largest waterfall by vertical(垂直的) area may be Victoria Falls, which sit on the border between Zimbabwe and Zambia, but it's South America that's home to the world's tallest.

    Angel Falls, located in Bolivar, Venezuela, has an impressive, uninterrupted drop of 807 metres.

    It was actually named after the American pilot, Jimmie Angel, who first recorded it in his logbook on November 16, 1933.

Largest Area of Glowing Sea—Indian Ocean, near Somalia

    Bioluminescence(生物体发光) is the production and emission of light by a living thing and can be used to explain the surprising phenomenon(现象)of “glowing oceans.”

    It was in 1995 that scientists detected glowing sea in the Indian Ocean—just off the coast of Somalia-via satellite, The water was more than 250 kilometres long, and it was all thanks to the bacteria called phytoplankton.

Most Expensive Hotel Room—The Royal Penthouse Suite at Geneva's Hotel President Wilsom

    This particular suite is just the ticket, costing as much as US$83,000(£53,760)per night.

    But the high price will gain you access to 12 bedrooms and 12 marble bathrooms across 18,000 square feet.

    Security—for the information on your smart phone, as well as for the phone itself—is a hot topic these days.The truth is that you're packing a lot of sensitive information on your phone, and you should keep it safe.

    When it comes to physical security, iPhone users would do well to download Find My iPhone, a free app from Apple that allows you to visit a website and see your (lost, stolen or misplaced) phone on the map.You can then sound an alarm, send a message that will pop up on its screen, lock the phone or erase all your data.

    Android does not have an exact equivalent(等价物), but there are plenty of alternatives. A free app called Lookout offers the find­my­phone feature.The paid version allows you to wipe the data from your phone remotely.

    Then there is your coffee shop's Wi­Fi network.Anyone with minimal technical expert skill can snoop on(窥视) people using shared wireless networks, harvesting passwords and other personal data. Lookout will caution you when you've logged on to an insecure network, but cannot protect you once you're there.

    In order to protect yourself on such networks, you can use a virtual private network, or VPN. This turns all your activity into nonsense to anyone trying to read along with you from across Starbucks. It also keeps websites from tracking you and, if you're travelling, allows you to get access to sites that may be blocked in other countries.

    If you have an iPhone, the simplest VPN app is probably Hotspot Shield, whose distinguishing feature is said to be that it automatically kicks in each time you start browsing (浏览), as opposed to other VPN apps that require you to start them up manually(手动地)．This matters, because even if you decide you want a VPN app, you want to spend approximately zero time thinking about it. For the most part, that was true of Hotspot Shield, though occasionally it took a while to connect or temporarily lost connection without warning. I found myself having to turn the app on and off sometimes, which involved setting my phone constantly.

    If even reading about the settings on your phone drive you crazy, then it is probably best to stay away from a VPN app. But if you're the type who can't resist checking your bank balance from your corner bar, the hassle(麻烦) may be preferable to the risk.

    Sometimes people call each other “scared-cat”. But have you ever thought about this expression? When a cat is frightened, its heart starts beating faster, its muscles get tense, and there are changes in the chemicals in its blood stream. Although the cat doesn't realize this, its body is getting ready for action. If the danger continues, the animal will do one of two things .It will protect itself, or it will run away as fast as it can.

    Something like this also happens to people. When we are excited, angry or seared by other feelings, our bodies go through many physical changes. Our hearts beat faster, and our muscles get tense. All of these changes make us more alert and ready to react. We, too, get ready to defend ourselves or run.

    Human beings, however, have a problem that animals never face. If we give way to our feelings and let them take over, we can get into trouble. Have you ever said something in anger or hit somebody and regretted it later? Have you ever shouted at a teacher, told someone you were lonely, or said you were in love, and then wished later you had kept your mouth shut? It isn't always clever to express your feelings freely.

    Does this mean that it's smarter always to hide our feelings? No! If you keep feelings of anger, sadness hidden away or bottled up inside, your body stays tense. Physical illnesses can develop, and you can feel disturbed badly inside. It can actually be bad for your health. It isn't good to keep pleasant feelings inside either; all feelings need to be expressed.

    Feelings that you keep all bottled up inside, don't just go away. It's as if you bought some bananas and put them in a cupboard. You might not be able to see them, but before you'd smell them. And if you opened the cupboard, chances are that you'd see little fruit flies flying all over them. They are bad.

    You can try to treat feelings as if they were bananas in the cupboard. You can hide them and you can pretend they don't exist, but they'll still be around. And at last you'll have to deal with them, just like those bananas.

    Cities usually have a good reason for being where they are, like a nearby port or river. People settle in these places because they are easy to get to and naturally suited to communications and trade. New York City, for example, is near a large harbour at the mouth of the Hudson River. Over 300 years its population grew gradually from 800 people to 8 million. But not all cities develop slowly over a long period of time. Boom towns grow from nothing almost overnight. In 1896, Dawson, Canada, was unmapped wilderness(荒野). But gold was discovered there in 1897, and two years later, it was one of the largest cities in the West, with a population of 30,000.

    Dawson did not have any of the natural conveniences of cities like London or Paris. People went there for gold. They travelled over snow-covered mountains and sailed hundreds of miles up icy rivers. The path to Dawson was covered with thirty feet of wet snow that could fall without warming. An avalanche(雪崩) once closed the path, killing 63 people. For many who made it to Dawson, however, the rewards were worth the difficult trip. Of the first 20,000 people who dug for gold, 4,000 got rich. About 100 of these stayed rich men for the rest of their lives.

    But no matter how rich they were, Dawson was never comfortable. Necessities like food and wood were very expensive. But soon, the gold that Dawson depended on had all been found. The city was crowded with disappointed people with no interest in settling down, and when they heard there were new gold discoveries in Alaska, they left Dawson City as quickly as they had come. Today, people still come and go — to see where the Canadian gold rush happened. Tourism is now the chief industry of Dawson City — its present population is 762.

    It is a psychological strategy that all parents will be familiar with: instead of scolding an misbehaving child, focus instead in rewarding them for good behaviour.

    Now the idea is well received outside the nursery, with implications for everything from recycling clothes to policing.

    Consumers end up with piles of unwanted clothes. Every year in the UK, 300,000 tonnes ends up in landfill — 235 million individual items.

    Now however, apps such as ReGain, Regive and Stuffstr are making it simpler — and more worthwhile — for people to return their unwanted clobber.

    The ReGain app can be used to find one of 20,000 drop-off points. In return, the diligent consumer earns rewards such as discount coupons for high street retailers. Stuffstr works in partnership with John Lewis to help people get cash in return for unwanted items from the chain.

    “Possibly the one prediction that we economists get right is that if you incentivise (激励) a behaviour, you will get more of it,” says Dr Matthew Levy, a lecturer in economics at the London School of Economics.

    He cites research, including his own, showing that financial incentives encouraging regular exercise, stopping smoking and losing weight effectively promote healthy behaviours and that there is no backlash when the incentives are removed.“If anything, the incentives can be used to jump-start a healthy habit that keeps going,”he says.

    In the four months after its launch, the ReGain scheme received almost 17,000 parcels containing 47 tonnes of used clothes and shoes, of which 95% could potentially be reused, according to its founder Jack Ostrowski.

    “We need to find a way to influence behaviour, and discount coupons help,” he says. The platform is also working with brands and retailers to find ways to divert used clothes from landfills and into the production of new clothes, he adds.

    Other reward schemes have had success in encouraging behavioural change.

    When police in Canada issued “positive tickets”— coupons for free food or movie tickets — to reward good behaviour among young people, they reported an almost 50% drop in youth-related service calls.

    “My officers would say' In the old days we'd drive up in the police car and the kids would run away from us, now they run to us'.”

    In a similar venture, Hull city council have announced plans to launch a digital reward token — the HullCoin — that can be earned by volunteering and spent at local retailers.

    Elsewhere, a study on the recruitment of health workers in Zambia found that highlighting economic incentives during the recruitment process caused future employees to be more motivated and task-focused.

    “Obviously different groups are motivated by different factors,” says Ostrowski. “For some, the feel good factor is enough, and for others, that reward stimulus is required.”