The news arrived late on Saturday afternoon. My wife found three tickets under €100 for a return Sunday trip to London to meet our daughter Siofradh for lunch. Not an overnight stay, just a full, laissez-faire day in one of the world’s great cities with time for breakfast, a wander through galleries, a proper walk, maybe a pint in a storied pub, and the low-key, budgetary satisfaction of returning home that same night.

It’s surprisingly easy, as it turns out. Our Ryanair flight lifted off just after 6am and a late return from Stansted gave us around 15 hours in the city. We travelled light: a phone, a charger, a passport, and it was London calling.

We arrived at Liverpool Street Station early, having picked up a combined Stansted Express and London Travelcard (about €28 each on a group of three fare). Directly across the pedestrian crossing from the station is Polo Bar, a 24/7 dining spot. On the ground floor, it’s a neon-lit temple of confectionery and takeaway, but we wanted to linger. Up a tight staircase, the space is narrow, snug and pleasantly frayed, brimming with a sort of Kray-era charm. Local families, and some still on Saturday night mode, huddled over Formica tables, sharing space with “full-on” breakfast baps laden with sausage, pudding and eggs.

From there, we used Liverpool Street to get to Bank Station. As we meandered through the city, we passed through squares filled with sculptures. In Paternoster Square, just north of St Paul’s Cathedral, we found the “Go Wildlife Go” sculpture. It features 13 endangered animals, including an elephant and a giraffe, on a giant bronze scooter.

The early-morning calm is a gift: St Paul’s dome towers above, suddenly immense, the streets mostly our own until St Vedast-alias-Foster bursts into a melody of bells. Bow Lane, a curling medieval street filled with old-world pubs and atmospheric shops, lures us in. Midway, St Paul’s is framed by the low-lying streetscape that captures the magnificent dome like living architectural art.

Nearby, at Fen Court, the Garden at 120 fell in with our fluid plan. A smooth rise by lift (free admission, check opening times) opens to a stretch of open terrace where the city’s jagged skyline surrounds. St Paul’s sits steady in the distance, the Thames threads its way through, and the glass towers feel less severe from here. The Gherkin’s curve catches the eye, and the Shard stands further off, yet still part of the same view. It’s a calm space, even off-season; a place to pause, look out, and let London come back into focus from a different angle.

Westminster called, and short of a hug from Paddington Bear, no moment marks your arrival in London quite like the slow ascent from Exit 4 of the station as Big Ben rises above you.

On the bridge, thousands darted back and forth to snap the London Eye or that epic shot of the Houses of Parliament. We didn’t linger – well, just long enough to take our own photographs – before we moved towards Leicester Square Station.

A short walk brought us to Bar Italia in Soho. It was Anthony Bourdain’s favourite coffee haunt. It’s a little shabby in the best sense: neon lights, quirky art and the sense that space is at a premium. And yes, maybe it was the Bourdain legacy or the time of day, but the coffee was superb. Across the road stands Ronnie Scott’s Jazz Club, a Soho landmark, silent at this hour, sleeping off a cocktail of whiskey, blue notes and backbeats.

London is at its richest in contrasts. One minute we’re walking down Brydges Place, a street that’s little more than a foot wide in parts; the next moment we’re in the vast halls of the National Gallery looking at JMW Turner’s The Fighting Temeraire. The painting shows the ship in 1838 on her final journey, towed along the Thames by a dark industrial tugboat against a yellow-red tinged sunset, symbolising the end of an era.

By this stage it’s lunchtime and we slipped down a side street for something shaken, not stirred. Dukes Hotel is the place for a James Bond-style martini – all precise mixologist’s ceremony and old-world charm – but it was our first plan-free casualty: the bar was closed for the day. The American Bar at the nearby Stafford Hotel, however, is another living time capsule. It offers a decadent “Seven Deadly Sins” menu that includes martinis and whatever else you’re having yourself.

We headed back towards the light and pulse of Piccadilly for a quick rummage at Fortnum & Mason, who have sold delicious treats at their flagship store here for more than 300 years. We weren’t tempted to buy any of their produce, courtesy of Ryanair’s carry-on policy. Hatchards, which has been its neighbour a few doors down for most of that time, took a slice of our afternoon instead. First editions of Joyce quietly hum with history beside Steinbeck and other rare prints priced in the thousands of pounds.

This made a late lunch at Wong Kei in Chinatown a rushed affair, filled with nostalgia, Cantonese roast duck on rice and famously brisk service. History is never far away; the John Snow pub (no, not that guy) in Soho stands near the infamous Broad Street pump, the epicentre of London’s 1854 cholera outbreak. Snow discovered the source and it’s a reminder that even the streets beneath our feet have stories to tell.

By late afternoon, the pace slowed. We took a short wander and a chance to reflect on the city’s layered streets around Covent Garden. The market, a neoclassical masterpiece, is now filled with high-end merchandise, but there are still treasures to be found beneath the colonnades along its perimeter. A jacket potato and coffee from Peter’s Snack Bar is best enjoyed across the cobbles and through the timbered doors to the garden at Covent Garden’s St Paul’s, known as the actors’ church. Here, benches sit among neat hedgerows in what is almost a sound-vacuum from the performers around the market; a quiet pause to say goodbye and make tracks home.

By the time we lifted off over Essex, London had shrunk again to rooftops and lights. Fifteen hours had stretched comfortably across centuries of history, culture and urban life, and we were home by bedtime, our last-minute, schedule-free city adventure complete.

Budget

In total, with flights (Dublin, Cork and Shannon offer almost identical service), food, transport and a few indulgences, the day can be done for around €130-€150 per person; add a theatre matinee or a cocktail at Dukes and you’re looking at €150-€200.

Ground transport

To save your legs and see more of the city, hop on the number 88 bus. For £1.75 (€2), it’s effectively a budget sightseeing tour. From the open deck upstairs, Piccadilly, Whitehall, and Westminster pass by like a cinematic reel. With an all-day Stansted Express Group Save purchased at Stansted (€28), you get the return train to the city plus unlimited buses and Underground travel.

Sunday theatre

If theatre appeals, Sunday matinees are ideal. Most West End theatres do not run evening performances on Sundays, so an early-afternoon show fits neatly into a day trip. Popular options include The Lion King, Les Misérables, Wicked, or Matilda the Musical. Tickets can be found through TKTS Leicester Square for same-day discounts, or via official theatre sites, with day seats often starting around £25 (€30).

No lunch reservations? No problem

(1) The American Bar at The Stafford (16-18 St James’s Pl, SW1A 1NJ), a high-end 1930s landmark with mains from £20-£35 where walk-ins are welcome for bar snacks.

(2) Nearby, head to the Art Deco basement of Brasserie Zédel (20 Sherwood St, W1F 7ED) for a £17 set menu in a grand Parisian setting that rarely requires a booking.

(3) In the heart of Soho, The Coach & Horses (29 Greek St, W1D 5DG) offers famous ham sandwiches and pub fare for £10-£18 with no reservations needed.

(4) Bar Italia (22 Frith St, W1D 4RF) provides historic Italian bites for £7-£15 at its walk-in counter.

(5) Rock & Sole Plaice (47 Endell St, WC2H 9AJ) has served classic fish and chips (for £15-£22) since 1871.