Buried under the wonderful Hotel San Carlos is the perpetually popular Seamus McCaffery Irish Pub. I'm not a big drinker (actually, I don't drink, but I used to) but I love going to bars. There is something about the ambiance of a good Irish bar that doesn't try to be more than that. McCaffery's has a pretty decent menu for a bar. Corned beef and cabbage and fish and chips are expected but uncommon in the downtown area which makes them welcome fare. The beer selection is excellent with tons of imports in bottles and on tap. The burgers aren't great but the tuna sandwich is killer. There is live music on the weekends usually and the crowd is pretty constant most nights.
The service is terrible but it's a bar, I'm not sure what you expected.
If you are looking to drown your sorrows or surround yourself with a blue collar crowd, this is the best place in town to do it. If you are looking to grab a bite to eat, the Silver Spoon next door is a safer bet for variety and service.