As the snow wafts down and the forecasters warn of arctic conditions to come, spare a thought for the folks of ancient Edo, who had to make it through the winter months without such essential survival tools as fleece jackets, cup ramen and Hokaron hand warmers.

In the absence of central heating and double glazing, their guiding principle was always “heat the person, not the room.” Thus thick hanten jackets to keep the top half cozy; kotatsu heaters to toast the toes; and hearty, nourishing food to stoke the embers of the inner metabolism.

Even today, nothing is as effective as a nabe, the meal that heats you several times over — first as it cooks; then as you eat it; and most of all from the sense of conviviality that eating around a communal stew pot inevitably engenders. At this time of year, you don’t have to travel far to find nabemono on the menu. But nowhere demonstrates this traditional winter wisdom better than Isegen.

Not so much a restaurant as a very tangible national treasure, Isegen is one of a very small cluster of timber buildings in Kanda’s historic Sudacho district that miraculously managed to avoid the 20th-century triple whammy of earthquakes, fire bombings and urban development. Though the current structure dates back only to the early days of Taisho (the 1920s), Isegen has been in continuous operation for 150 years.

During that time it has only served one kind of food (in the winter months, at least) — bubbling casseroles of anko (monkfish, angler, lotte de mer), a fish whose tender white flesh is as succulent as its visage is ugly. In Europe monkfish is considered gourmet fare, but here anko nabe has always been a food of the common people, as simple and as straightforward as a bouillabaisse and one of the essential pleasures of winter in shitamachi.

Unless you are a group, Isegen does not take reservations. It’s first come first served and if all the tables are taken, you’ll be given a number and asked to get in line outside. Even with its new annex, which has more than doubled the seating space, such is Isegen’s enduring popularity the only way to avoid a wait is to arrive early (before 6 p.m.) or after the main rush (8 p.m. or so).

Finally you will be summoned into the paved genkan with its massive Shinto altar and ceiling panels made from the designs on old sake casks. Leave your shoes with the doorman and make your way up the polished wooden stairs. The new rooms at the back (usually set aside for groups) are in traditional style but lack patina. Instead, ask to be seated in the main dining room, a large, well-worn, tatami-covered area occupying the entire second floor of the original premises.

The concept of personal space was never a consideration in Edo times, least of all in winter, and part of the whole Isegen experience is that you are shoehorned in, cheek by jowl with your neighbors. You will be ushered to a low-slung, scuffed, red-lacquered table not much bigger than the four zabuton cushions which surround it. Save for the battered gas ring and aluminum nabe on top of it, everything looks much as it must have done half a century ago.

Your nabe is served almost as soon as you sit down. You have no choice in the matter — they only serve one kind and that’s what you’re there for anyway. There is little more selection when it comes to the drinks: beer; sake, either hot or cold; shochu; cold soda or hot tea. But do take note of the small menu detailing a number of extra tidbits you can nibble on while waiting for your pot to boil.

Try the kimo-sashi, small slices of the creamy-orange liver of the fish (1,300 yen); served raw with a ponzu dipping sauce, its exquisite, smooth, rich texture never fails to conjure up comparisons (in most people’s minds favorable) with the best foie gras. Or order a serving of delectable white anko flesh, just three small morsels but memorable for their delicacy, cooked up in teriyaki or kara-age style (each 1,100 yen).

By this time your nabe will be bubbling away nicely. Besides more slices of an-kimo (anko liver) and chunks of white tail meat, you will find it contains globs of blubber-like mune (fat from the belly) and squares of black, gelatinous kawa (skin), both of which are more acquired tastes; plus cubes of tofu, shiitake, assorted vegetables (snow peas, negi, udon and mitsuba); and shirataki noodles. The warishita broth is already flavored with shoyu, so no further dipping sauce is provided: Just pick out whatever you like the look of and consume.

Should you feel less than replete, it is perfectly in order to call for second helpings of the fish alone (3,000 yen); just the tofu and veggies (1,000 yen; ask for zaku); or the whole thing again (another 3,300 yen per head). But the best way to fill up is to ask for ojiya. More broth will be brought, into which cold cooked rice is mixed, then a beaten egg is stirred in, to form a thick, stick-to-your-ribs porridge, topped with a mound of fine green scallions.

All this is performed for you by the kimono-clad waitresses, no-nonsense souls of a certain age who are never too busy to dispense a word of advice or admonishment (“Don’t poke your ojiya till it’s ready!”).

This is all part of the Isegen experience: Everyone is eating the same thing, everyone’s on the same level and all are united in a sense of communal bonhomie.

When you have finished you descend to the lobby and squat down to pay at a window set at about the height of your knees. The white-haired gentleman who sits here at his cash desk, greeting the customers and observing everything, is Isegen’s fifth-generation owner. He accepts cash only, just as it’s always been since the very beginning.

The anko season lasts from October through March. After that Isegen specializes in river fish — carp, ayu sweetfish and that favorite of all true children of Edo, dojo (eel-like loaches). The building remains no less atmospheric and the welcome no less warm. But somehow the true spirit burns at its brightest when the weather is at its coldest.

If you are faced with a long wait at Isegen, one way to keep warm is to explore the neighborhood. Just round the corner you’ll find Botan, (03) 3251-0577, the most venerable chicken sukiyaki shop in the city. The nabe recipe here hasn’t changed in a century, it’s still cooked over charcoal and the premises are creaking with history. But they’re often so busy that the production-line service can feel impersonal.

One block away is Yabu Soba, (03) 3251-0287; set within its own little compound, this is the Ise Jingu of buckwheat noodles. And then there’s Takemura, (03) 3251-2328, the wonderful ancient tea shop right across from Isegen. Perfectly situated, in fact, for an after-dinner cup of green tea and a sweet red bean confection (though you will need to finish eating no later than 7:30 p.m.).

In line with COVID-19 guidelines, the government is strongly requesting that residents and visitors exercise caution if they choose to visit bars, restaurants, music venues and other public spaces.

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