There are several different options available for visitors wishing to go on an expedition in Greenland. Certain travel operators offer globetrotters possessing a spirit of adventure the chance to cross the ice sheet. It is also possible to put together your own expedition, but in some cases you may have to apply for authorisation first. This applies, for example, if your expedition plans to cross the ice sheet or to take in part of the National Park in Northeast Greenland, in which case permission is required from the Danish Polar Center in Copenhagen.