After the Plaza de Armas, the malecon, and Belen, there is little else to do in Iquitos proper. If you have can spare half day, as many do when arriving or leaving for a stay at one of the area's many jungle lodges, there is a great relaxing excursion to the Pilipintuwai Butterfly Farm that will disappoint very few.
The farm is set in the village of Padrecocha. You can catch a water taxi from Puerto Bellavista, either with the slowboat or the speedboat. From there, depending on the season, you can either walk right up to the lodge or, possibly, hike a short distance through the village. If you get lost just ask for "Las Mariposas."
The farm's main focus is the butterflies it helps breed. There are more than 40 different species found there. A short tour will take you to each stage of metamorphosis, from caterpillar through the complete cycle to butterfly. A walk through an enclosed area where each species of butterfly is happily floating around in a lush, plant-filled garden is the highlight. Pilpintuwasi is the only butterfly farm in Peru.
Pilpintuwasi also has a few rare animals that were abandoned, mistreated, or rescued from the area. These include a giant anteater, a river manatee, a tapir, a jaguar, and a few very friendly monkeys.
A roundtrip shouldn't take more than a few hours and it gets you out of the city, which is probably the reason you came to the Amazon rainforest in the first place. Visit www.amazonanimalorphanage.org/pilpintuwasi.htm for more information.