No quests are in there, but it leads to several places if you can get past the guards there.
Japan (checked)
China (checked)
South pole (checked)
Maya (a guess from the name/appearance of its guard)
Revival island (a guess from the name/appearance of its guard)
Calcutaa (a guess from the name/appearance of its guard)

Also, the places the tunnels lead to seem to be lined up with holy. (japan to the north, south pole to the south south, etc.)

I was able to get to south pole with my character (lvl 51) and three lvl 24-29 friends. The ones to japan and china are a bit harder since the enemies actually use attack skills, so it's a good idea not to go alone.

If you're on the cancer server, I can take you to japan and you'd only have to fight the first guard with me. There's a way around the second guard.