No, you need an internet connection to start playing. Then you will find an offline dungeon (without coop) at the north of the map. Maybe in next updates I will add a full/real offline option to play :)
Ah, I have found the northern offline dungeon. Is a new offline dungeon generated every time you enter, while the co-op dungeon always has the same layout?
Exactly! The north is just offline and full random every time you enter (like a regular RL). The dungeon on the right is the coop mode. Same dungeon seed for everyone until someone manage to win the dungeon (then a new one its generated)