More Adventures
The adventure continues in the DM's booklet, detailing more of the dungeon. Things get slightly more complicated as the adventure progresses. You have a magical altar with baneful effects; there are chests with traps and treasure; and more dangerous monsters are encountered, some with special abilities like the harpy's captivating song.
Eventually, the PCs will reach second level, which is described in the Advanced Rulebook, and finish the adventures in the DM book. That leaves them with one task: to slay the blue dragon behind all the adventures.
Cheers!