This building has been a part of Reykjavík dining since 1932. It has gonna through a lot of changes through time, yet there has always been food-related activities in the building (even McDonalds for a while). They have great coffee and a lovely patio.
I haven't been so impressed with the food there, but it's perfect for drinks (coffee and alcoholic beverages). It has a long and interesting history, being one of the oldest houses in Reykjavík (built 1805).
Grab a seat in the patio on a sunny day.