Østerbro is Copenhagen's elegant residential quarter — 1900s apartment blocks for the rising bourgeoisie, the lake's east shore on its southern edge, the diplomatic spine of Dag Hammarskjölds Allé, and the Svanemøllen harbour at the top. The walk runs the length of it.
Three and a half kilometres, a hundred minutes if you walk slowly. Start at Trianglen — the square at the south-east corner of Fælledparken — and drop south down Dag Hammarskjölds Allé, the broad embassy-lined avenue. The eastern lakeshore at Sortedam Sø is fifteen minutes south; walk the willow path for a stretch.
Back up through Østerbro via Strandboulevarden, the residential spine. The apartment blocks here are the city at its most bourgeois-elegant — bay windows, copper details, the rising mercantile class made permanent in stone. Most are still residential; a few have become embassies.
End at Svanemøllen (Swan Mill) — the S-tog stop at the northern edge of Østerbro, with the small recreational harbour behind it. The closing image is water and sailboats and the city behind you.