Früh am Dom is the most famous of Cologne's traditional brewpubs, sitting across from the cathedral since 1904. It serves Früh Kölsch — one of the city's most respected brews — directly from barrel, carried by Köbes in the traditional Cologne waiter style: a round tray of glasses, delivering and collecting without being asked. When your glass is empty, another appears unless you place your coaster on top to signal you are done.
The food is traditional Cologne cooking — Himmel un Ääd (blood sausage with apple sauce and mashed potato), Halver Hahn (a rye roll with gouda), Flönz (blood sausage), and hearty meat dishes. The atmosphere is convivial and loud and the tourist density is high, which does not diminish it. This is genuinely what Cologne food culture looks like. The building has multiple rooms and levels; aim for the older sections rather than the newer extensions.