Some of the world's great tourist attractions are being ruined

Travel industry insiders say 2015 is going to be the biggest travel summer in years -- but all those people hitting the road means many thousands of feet on the ground, tour buses cranking out fumes, hikers leaving garbage on trails (you get the picture).

And while tourists are generally a good thing for local economies (they do love to spend cash, after all) some countries are debating whether or not to put a cap on tourist numbers. They're trying to balance conservation and tourism -- not always an easy feat.

Over 10 million people a year visit the 5,500-mile long Great Wall of China. Some tourists are disrespectful and do everything from carving their names in the wall's stones to spraying graffiti.

Cambodia's stunning Angkor Wat temple attracts 2 million tourists a year. UNESCO officials say tourists regularly "step on stones and carvings."

India's Taj Majal not only has to fight air and water pollution, but the traffic of nearly four million people a year. The marble and sandstone in some areas of the monument are eroding faster than ever.

And those aren't the only places at risk. The art in the Vatican's Sistine Chapel could be Michelangelo's greatest achievement. But, all the carbon dioxide that tourists breathe out are doing damage. Not only that, but the dirt, dust and yes, skin flakes, that the five million visitors a year sprinkle all over it are also ruining things.

In 2012, the Vatican promised to take a Dirt Devil to tourists saying that they'd "install suction vents to suck dust from clothes" and lower temperatures to reduce the heat and humidity of bodies. Some other sites have gone to even more extremes.

King Tut's tomb in Egypt was closed to tourists completely after moisture from years and years of visitors caused the tomb to deteriorate.

But, experts say that sustainable tourism on a big level is possible and really starts with small actions. So please, don't touch the paintings, don't scribble on the Great Wall like it's a bathroom stall at Hooters, and if a tourist site seems just too crowded, take your dusty pants and skin cells off the beaten path.