Inside the Taco Stand in Wynwood, a small silver keypad hangs next to a bare copper wall. Enter a secret code, and the wall becomes a sliding door. It opens slowly and carefully, revealing a covert room fit for no more than ten people. This is Hiden, a mysterious omakase restaurant where $130 will get you 15 courses of fish flown in from Japan. Dining here requires reservations. Once you book a meal, you receive a four-digit code granting access to the private sushi den. Walk through the taco joint, blaring with mariachi music and steaming with the aroma of freshly fried tortillas, toward the back of the restaurant, where the copper door beckons. There are no menus. Your meal will be in the hands of Brazilian-Japanese executive chef Tadashi Shiraishi, who will decide what to serve only hours before your arrival. Traditionally, he offers two cold appetizers, a soup, seven to eight sushi courses, a hot item, and dessert. The two-hour experience is limited to eight diners, and seatings are at 7 and 10 p.m. Saturday through Sunday.