Start with St. Paul’s Cathedral while you’re still in the historic heart of London. Since it’s late, this works best as an exterior visit or, if timings line up, the evening service rather than a full interior tour. The dome is especially striking in the soft evening light, and the area around Paternoster Square gives you a clean first look at the City’s mix of old stone and glass towers. If you do go inside on another day, standard entry is usually around £25, but for tonight keep it simple and enjoy the setting for about 45 minutes.
From there, wander across Millennium Bridge for one of the best easy skyline walks in the city. It’s only a few minutes on foot from St. Paul’s Cathedral, and the view back toward the dome is the classic shot people come to London for. This is also the most natural way to drift toward the South Bank without feeling like you’re “doing sights” too hard on arrival night. Keep the walk relaxed — it’s only about 20 minutes, and the riverfront at this hour is usually lively but not overwhelming.
Head on to Tate Modern for a low-key first evening stop. The museum is free, which makes it perfect for an arrival day, and even a quick hour gives you a good feel for the building and the energy of Bankside. If the galleries are still open, pop into just one or two rooms rather than trying to cover everything; the point is more to settle in than to exhaust yourself. It’s an easy walk from the bridge, and the surrounding riverside paths make a nice buffer before dinner.
For dinner, book or walk over to Padella in Borough Market if you can get in — it’s one of those places Londoners still happily queue for, because the pasta is reliably excellent and the prices are fair for the area, usually about £20–30 per person with a drink. Afterward, if there’s still energy and the market stalls are open, take a final wander through Borough Market for dessert, a glass of wine, or just the atmosphere. Even a short loop through Borough High Street and the market arcades gives you that immediate London feeling: busy, slightly chaotic, and full of good smells. If you’re arriving late, don’t worry about doing it all — this day is really about a gentle walk, a good meal, and leaving some room to settle into the city.