i think it was either Snow or Chet mentioning they saw something to you after either of their quests, still, from my guide: 

"This quest can be started from day 10, only if you have either followed Snow to the lake (“fishing with Snow”) OR completed Chet’s fetch quest for ectoplasm (the one unlocked after “Witer’s nightmares” and found under “about the work” not “new item quests”!). (Learning the holy fist skill in “Witer’s nightmares” is in your best interest to fully explore the dungeon (...))

An option to explore a new island should pop up in the forest where you met Thane/fight the bulls, this unlocks a new place on the map, to the south of that forest. (...)"

There you will find a hut and meet a new character, he will unlock the way to the first dungeon and all that.