Antoni Gaudí's unfinished basilica, a UNESCO World Heritage Site under continuous construction since 1882, is Barcelona's most iconic landmark. A guided tour reveals the symbolism behind its soaring tree-like columns, kaleidoscopic stained-glass windows that shift from warm to cool tones as the sun moves, and three intricately carved façades depicting the life of Christ.
Suggested time: 1.5–2 hours (guided tour)