The name St. Arnold refers to the Patron Saint of Brewing, and he doesn't disappoint! This is a great spot for happy hour. They have mussels and frites for only $9.99 from 4-7pm, and it's not a tiny happy hour sized portion either. That's got to be one of the best deals in the city for mussels. There are 5 or 6 different preparations; we had the one with white wine, capers, bacon, and leeks which was excellent.
St. Arnold's has a sizable Belgian beer list and runs beer specials during happy hour, although I may have enjoyed one too many Ommegangs because I forgot exactly how much they cost.
The space is in a dark basement and is on the small side, but the service, food, and drink were excellent.