Based on my interpretation of the subsequent verses, I think Dhu al Qarnayn probably means Lord / Conqueror of the Two Poles, i.e. the polar regions of the Earth, except that he already had this title on the first visit described, as he is being addressed as 'Ya Zal Qarnain'. However, since he is being addressed by the author of the story, it is also plausible that he was already destined to be the Lord / Conqueror of the Two Poles.
There is no land at the North Pole. ‘The Arctic consists of ocean that is largely surrounded by land. As such, the climate of much of the Arctic is moderated by the ocean water, which can never have a temperature below −2 °C (28 °F).’ 
The lands near the North Pole, in the Arctic Circle, are known for hot springs and geysers, with muddy water spewing out of some.      However, such places are also there near the South Pole, though perhaps lesser in number or less discovered.    Therefore, hot springs and geysers may not be a uniquely distinguishing feature of the North Pole from the South Pole. Hence, I’m inclined to think that ‘ainin hamee-atin’ refers to the warm waters of the Arctic Ocean.
[Al-Qur’an 18:89-90]   Then followed he (another) way,  Until, when he came to the rising of the sun, he found it rising on a people for whom We had provided no covering protection against the sun.
[Al-Qur’an 18:91] So (it was). And We knew all concerning him.
Appearing or Rising Sun?
People dwelling there? Land?
“The Antarctic Ozone Hole was discovered ... Satellite measurements then confirmed that the springtime ozone loss was a continent-wide feature... The ozone hole is formed each year in the Southern Hemisphere spring (September-November) when there is a sharp decline (currently up to 60%) in the total ozone over most of Antarctica.” 
“The severe depletion of the Antarctic ozone layer known as the “ozone hole” occurs because of the special atmospheric and chemical conditions that exist there and nowhere else on the globe” 
Legends and adventure stories also abound about the inner Earth, of creatures/people dwelling within the Earth. Though modern science refutes ideas about a hollow earth, if there is any figment of truth to any of these accounts, then it is a wonder why we humans have not been able to dig through or find a way to their subterranean civilization, or why they haven’t been able to reach up to the Earth’s surface, unless there exists a natural barrier with only one opening, which was sealed by Dhu al Qarnayn.