Some say that the 520 foot wide natural tunnel in the mountain was
created in the ice age due to the processes of freezing and erosion.

According to the Torghatten web site, the truth is that the troll
Hestmannen shot an arrow after the young girl Lekamøya who ran away
from him. The arrow went straight through the Troll-King's hat forming
the hole and as the sun rose, everyone was turned into stone.

Who are we to argue?