This was my favorite restaurant in Sevilla and I went there several times with friends. Photos of three different visits are below. I always went to San Marcos on Calle Cuna, but there are also 2 other locations. The extensive menu comes in both Spanish and English, that was great for helping me learn translations.
There are 3 different dining areas and although it is always busy, there is usually a table available for a party of 4 or less without much wait, however it is probably better to make reservations. Our dining experiences were always lengthy affairs as is the case for most diners there, though this isn't a reflection of the service which was professional and outstanding, but more a Spanish tradition. One time we dined until 1am and though they never mentioned they wanted to close, we realized we were the last ones there and exited shortly.
The ambience is upscale but comfortable and diners are fully relaxed and conversational. The bright magenta walls add to the character of the atmosphere. The cost of a gourmet meal here is very reasonable by American standards.
However the best feature of San Marcos (as it should be in a restaurant) is its fantastic cuisine. Pasta, fish, fowl and meat dishes abound along with several vegetable accompaniments. The appetizers are superb especially the carpaccio options and the salads (carpacio de salmon with black capers and the Gorgonzola salad were my favorites in these groups). I could have eaten there every night during my stay and still not have been able to try all the entrees. Fortunately each of my friends ordered different entrees and so we had ample opportunity to taste several different dishes. However, I was enraptured by the salmon au gratin over spinach with mushrooms and had to order it again. Another time, I enjoyed a big piece of beef fillet called solomillo de ternera which I requested be cooked crudo (rare) and it came out just how I like it. On one occasion, my friends enjoyed lamb, monkfish and lasagna. The lamb was tender, but had a strong taste and was accompanied by cous cous and mint. The monkfish was also tender and similar to grouper, but a stronger tasting fish. The lasagna was interesting with a sweet flavor to it.
Several choices of desserts and wines were also available. My favorite desserts contained chocolate mousse and were the Marquesa de Chocolate - a square of firm chocolate mousse wrapped with a sponge cake and the Blanco y Negro - a very sweet chocolate mousse with pastachio wrapped in whip cream with a spongy texture. We had excellent red wines and probably the best was a wine of the house for 9 Euros called Vina Fronda Rioja. As I write, I am craving again those exquisite dishes and fondly remembering all of my wonderful experiences there.