Den Gyldne Svane - part of a museum and very serious about their food. Presently they are cooking like it's 1401 AD. It's a restaurant for everyone in the day time and only open for parties on request at night.
La Casa Grande - My spanish isn's sufficient to tell you what's on the menu, but I do know that they offer a medieval experience in a big banquet hall fit for queens and kings. If you can't afford the castle this is difinately an option. From what I can gather, it's a part of a museum.
Gallo Nero - I don't know any italien, but their website caught my eye.They have a medieval menu for a medieval couple and nice rustic surroundings with dark wooden tables and candlelight.
Restaurant Cosy - is situated near the castle Chateau Bouillon and also offers rooms for the night. They also have a very fine describtion of how a medieval banquet would unfold, the seriation of the courses and what medieval source they use for their recipes.
Olde Hansa - in Tallinn is a beautiful restaurant with a wide range of choices for your wedding banquet, such as Royal Hunting Feast or Merchant Guild's Saturday Feast. They also have a small shop and live medieval music from time to time.
L'Auberge du Dragon Rouge - yet another medieval restaurant with the facilities to hoist a wonderful medieval party. They offer 5 different banquets, but you better check out their website yourself :) my french isn't the best either.
Rozengrâls - lies in the city of Riga and on their menu they have small explanations of where they got the recipe from. It's my impression that it's a big place that could easily acommodate a wedding party.
Please do write to me if you know of any restaurant that offers the same medieval magic in your country so I can add it to the list.