The most unique aspect of Luxembourg is the dramatic valley that runs through the centre of it, and the Pont Adolphe is one of three main bridges that connect one side of the city to the other. I walked over it on my way to the old city from the train station, admiring the incredible views across the city and down into the valley. Later, I took some steep, old stone steps from the edge of the Pl. de la Constitution into the Petrusse Valley and walked through the park next to the little stream. This walk ended up being the highlight of my trip, especially walking under the huge Pont Adolphe. It was built between 1900 and 1903 and is the largest stone arch in the world. Definitely walk across it to view the valley from above, but also don't miss the experience of walking at the base of the valley, despite the steep hike back up!