Iquitos is in the Amazonas region of Peru. This is not to be confused with the Department Amazonas where Chachapoyas is located. Iquitos is the capital of the vast Department of Loreto, which covers most of the northern Amazon region of Peru.
The main reason to visit Iquitos is that it serves as a launch point for trips into the Amazon. You are taken out on a boat and can view wildlife such as monkeys, alligators, giant lily-pads, baby caimans (sort of like mini-alligators), anacondas, boas, tarantulas, and more.
If you need to know regular companies or guides and their record of complaints, feel free to contact iperu, the government tourist information office. Their nationwide service is free and reliable and they may assist you in case you have problems or need to do procedures anywhere over Peru. The Iperu address is 161 Napo street (right off from the Main Square) and they open including on holidays, or contact them by phone (+51 65) 23-6144 or their 24 hours line (+51 1) 574-8000 or they email email@example.com. In iquitos, they work from Monday to Saturday from 9AM to 6PM and Sunday from 9AM to 1PM. They have an office in the Arrival Lounge of the Iquitos' Airport.
* When you exit the airport you will be approached very aggressively by the drivers. The drive from the airport to the city center is around 30 min, and prices are fixed at 20 Soles (USD 7) for taxi and at 10 Soles (USD 3) for mototaxis (tuk-tuk). Anyone offering a lower price will likely try to take you to a hotel or hostel that pays them, as well as sell you "the best tour company ever". In most of the cases you can get scammed. If you already have a hotel in mind, stay firm and they will take you there. Do not pay attention those people and check for reputable companies in Internet or iPeru.
* Do not eat endangered species. Some locals do so as tradition, but many "guides" (pseudo-guides) and restaurants will offer you to taste caiman, majás, turtles, deer and other "carne de monte" (wild meat). Remember breeding farms for these species do not exist, so these animals come from natural environments.
* It is advisable to steer clear from street vendors and the market places for your daily meals. Even though the food may look delicious (and it really is!) it is wise to stick to eating at professionally run restaurants. Eating in the street or at the market probably won't make you sick, but when it does, your vacation is ruined.