Luxembourg

The Bock Casemates, hollowed into the cliff face from 1644 onward under successive Burgundian, Spanish, French and Austrian occupations, run 17 kilometres through the sandstone — visitors can walk a signed section of tunnels and gun galleries that open directly onto the Alzette valley below, a genuinely disorienting sense of a fortress turned inside out. The Wenzel circular walk threads roughly a thousand years of wall-building in one loop, starting at the Bock promontory, descending into the Grund valley past the abbey of Neumünster, and climbing back up through later fortification rings — a practical way to see the full defensive system's evolution in one walk rather than piecing it together from separate stops.

The Chemin de la Corniche, a rampart-top promenade often called Europe's most beautiful balcony, runs along the old town's cliff edge with an uninterrupted view down to the Grund and the abbey of Neumünster below — most dramatic at golden hour, when the valley's church towers and rooftops catch the light. Getting between the plateau and the valley floor doesn't require the old stepped paths: the free Pfaffenthal panoramic lift and the Grund funicular both connect the levels in under a minute, meaning a full descent-and-return circuit costs nothing beyond the time it takes.

The Grand Ducal Palace's flamboyant Renaissance facade, on Rue du Marché-aux-Herbes, opens for guided tours only in summer when the royal court decamps to Berg Castle outside the city — check current dates before planning around it specifically. Notre-Dame Cathedral, a short walk away, holds the crypt tombs of Luxembourg's Grand Ducal family; Place d'Armes, the old town's main square, is where the city's genuinely international population — nearly half foreign-born — visibly gathers at its café terraces through the evening.

Across the red arch of the Pont Grande-Duchesse Charlotte, the Kirchberg plateau holds the gold-towered European Court of Justice, the European Investment Bank's glass headquarters, and Commission and Council services — one of the European Union's three institutional seats, alongside Brussels and Strasbourg. Mudam, the Museum of Modern Art, occupies a luminous I.M. Pei-designed building grafted onto the star-shaped Fort Thüngen, whose own Dräi Eechelen towers house a separate fortress museum next door; the Philharmonie's white-columned concert hall rounds out the plateau's cultural cluster. The tram runs the full axis from the airport end of the city through Kirchberg to the old town, free like the rest of the national network.

South of the centre, Esch-Belval is the physical record of Luxembourg's 20th-century industrial economy before it became a financial one — two preserved blast furnaces, once part of one of Europe's largest steelworks, now rise directly over the University of Luxembourg's main campus, built into and around the old industrial structures rather than replacing them. It's a genuine counterpoint to the EU-institutional polish of Kirchberg, worth the short tram ride south for anyone interested in how the city's economy actually changed shape.