Frankfurt is defined by the Main River, where pleasant walkways can be found on both the north and south banks of the river, and foot travel across the wide river is made possible by two pedestrian-only bridges. The south sidewalk features an excellent view of the city skyline, while the north side has a large grassy area that sits between the river and main city center. One of the pedestrian bridges, the Eiserner Steg, and is located near the Rententurm, a guard tower that is the oldest standing building in Frankfurt. Once you cross the river, head west until you reach another pedestrian bridge, which crosses the river at the Städel Museum. This part of the walk takes you past many fine museums including the Städel, which showcases classical European paintings and drawings. Once you return to the north side of the river, you can then walk along the river's edge as far as the Eiserner Steg to complete the two-mile stroll.