Market square on Commerce has the two best Mexican restaurants for atmosphere and authenticity in the downtown area, MiTierra and La Margarita. They both feature sidewalk (outdoor) seating, strolling mariachis, separate bars, and mexican bakeries. The food is very good although not the best in SA. For the best you would need to venture outside the downtown area to one of the local spots such as Los Patios or La Fonda. Another would be Rosarios in Southtown (walking distance from Riverwalk and Alamo). Market square is on street level not on riverwalk level and is on the west side of downtown. The market features many shops and mexican imports as well as live music stages during special events. Plenty of music around the 16th of September. Enjoy your trip to San Antonio, home of the NBA champs San Antonio Spurs! I have lived here since '88 so feel free to PM me with any questions.