Iquitos is only reachable by plane or boat. It is a port "on" the Atlantic Ocean at the head of the Amazon - over 2,000 miles from the ocean - so not really on but "on". We flew there in order to get onto our boat early the next morning for a weeklong cruise on the Amazon and it's tributaries. We spent the rest of the day wandering through the market, and doing other things. It was a pretty serious port with big ships and lots of little boats. It is large city with close to 1/2 million residents.