The Strasbourg Notre-Dame Cathedral is the essential. Flamboyant Gothic masterpiece (12th-15th centuries), 142 m high — the world's tallest building from 1647 to 1874, and remained the tallest medieval church in the world. Inside, don't miss the astronomical clock (19th-century mechanism, apostles' parade daily at 12:30 pm, €3) and the panoramic platform (332 steps, €5, view of the German Black Forest on clear days). The Gothic stained-glass (12th-14th centuries) is exceptional. The central portal tympanum (Last Judgement) is one of Europe's most beautiful.
The Petite France (Grande-Île, UNESCO since 1988) is the most picturesque district: 16th-17th century half-timbered houses along the Ill canals. The tanners', millers' and fishermen's district. To see: Tanners' House, Pont Saint-Martin, locks. Dream photo location.
The Covered Bridges (3 medieval bridges + 4 13th-century towers, separating the Grande-Île from the fortifications) — the bridges were covered (wooden roofs) to protect the defenders, dismantled since. The Vauban Dam (1681-1690) houses a free panoramic terrace over Petite France — essential view.
The Rohan Palace (18th-century episcopal palace, late Gothic and Baroque) houses 3 museums (Fine Arts, Archaeological, Decorative Arts — €8 pass). The Alsatian Museum (traditional Alsatian life in 3 half-timbered houses, costumes, furniture, religion — €8) is the cultural essential. The Museum of Modern and Contemporary Art (MAMCS) and the Strasbourg Historical Museum complete the discovery.
The Neustadt (Wilhelminian extension 1880-1918, UNESCO since 2017) unfolds imperial German urbanism: Place de la République (formerly Kaiserplatz, with its monumental ensemble — National Theatre, Rhine Palace), University Palace, National and University Library (France's 2nd after the BnF), Aubette (SS headquarters during the war, now a restaurant).
The European Parliament (seat of the plenary session) and the Council of Europe can be visited for free (booking advised — guided tours in several languages, Monday-Friday).
The Batorama cruise (1h15, €14 adult) on the Ill is the tourist experience not to miss — passage through Petite France, the cathedral, Neustadt, the European quarter. Commentary in 12 languages via audioguide.
The Christmas markets (from late November to 24 December): 11 themed markets in the city (historic Place Broglie, Place Kléber with the 30 m giant tree, cathedral square, Place Gutenberg, Place Saint-Thomas...). Unique atmosphere in the world.