Old Isakayas (Tokyo)
could you recommend a good Isakaya in Tokyo? I'm thinking about an older building, lots of locals, kind of loud but really relaxed atmosphere. Does not have to serve Michelin level foods, I'm more looking for a fun place to hang out after work.
Tons of options downtown as was rightly noted by those who replied before me.
The first place that came to mind, and one of my favorites in Shinjuku, was Donzoko (http://www.donzoko.co.jp/).
The atmosphere is allegedly the same as it was in the 50's although I'd be willing to bet that fewer artists hang out there these days (Mishima and Kurosawa used to hang there). Mostly a young to middle-aged business crowd by my recollections.
If I remember correctly, there are four different floors--each one with its own vibe. The place is rambunctious in a tolerable way on most evenings, and the surrounding neighborhood has a number of other good evening-oriented options.
On the Yamanote line, 5mn by walk form Okcahimachi station, there is a 2 generation Izakaya named Yushima YUSUKE. Japanese popularity food around 3-4000.-yens.
After, if you want to try the local ‘oyaji’ place in Shimbashi and ‘kanda’, for an after work on a beer and small common dishes ... do not hesitate.
I really think you should specify where you work or live - there are just too many places, and inside Yamanote covers a lot more ground than most people would want to for an after-work thing.
The one Nini suggests here looks pretty good, and I've been to a couple others I liked around there (Koyu in Nezu was best; top class izakaya).
I actually don't recommend many things around my office (Otemachi, including Kanda, which I haven't had good luck with for izakaya), although there's Fukube in Yaesu, which is semi-recommended.
Since even Yaesu is technically outside the Yamanote (as are Ningyocho and Asakusa), I'll go all in and point out that Hatchobori and more importantly Monzennakacho have an unusual concentration of good izakayas. In Monnaka alone, you could fit that bill with Hanabishi, Fukuden, S&S, Ogawa, Daruma, Uomatsu or Issui, and I haven't even been to Uosan, which is what everyone else recommends.
Here's a Hanabishi review:
In Hatchobori, try Wadaya or Umi - both good food and great sake selections - or Denshou for chicken-based stuff in a friendly environment.
Finally, try googling 'izakaya sanpo' - he's got a nice site.