okay, so it's not exactly a secret underground fish market, because it was swarming with people, but i didn't know about it and i have no idea what it's called, so I'm taking the liberty to call it whatever i want. :) here's how you do it. first you stand on the walkway and eyeball the fish. peruse the variety and listen to the saleslady tell you how delicious and fresh her fish are. then you pick a couple of the fish you want, and then go in back. you sit on little tables behind the counter and eat the fish that you just picked and that the nice old ladies just cooked fresh for you. dinner straight from nature to your plate.
this secret underground market is nuts! it sits right on a river that leads to the ocean and is the busiest, most colorful, most compact area i have seen so far. you hear the water pumping to keep the fish fresh, smell the salt water and cooking fish. definitely not something you can find in boise, idaho.
also, this secret underground fish market is ruled by women.