It started as gliding down hills on low performance kites, but now pilots can stay airborne for hours, reach altitudes of several thousand feet and reach speeds of over one hundred kilometres per hour. To glide in this way the pilot must find rising air masses. The most common source of lift are thermals where the warm air, heated by warm land mass, raises upwards. There are other types of lift near mountains, hills and cliffs where the wind is deflected upwards. These wind currents and thermals are often unpredictable and this can make the sport dangerous. This is where training is so important, not only to learn how to fly but to understand the weather and know when to stop flying.