From the introduction:
The Curse of Zarzumotl is an “old school” adventure in the True World Maztica Campaign setting and it is roughly designed for levels 3-5. Though the plot is complex and there is an overall goal for the players, in many ways The Curse of Zarzumotl is a basic dungeon crawl. Many of the encounters here can be quite deadly if the adventurers are not careful and there are some encounters that only a fully rested, strategy minded party will be able to overcome. The DM should give the players plenty of opportunities to gather their resources between battles. It is recommended that the players are awarded levels at key moments in the adventure, rather than at each encounter, particularly if they manage to avoid some of the battles. It is also necessary for the DM to have a good understanding of the events in the adventure before running it.