I had walked the bridges that connect Manhattan to Brooklyn, Queens, and Fort Lee, and between Queens and Brooklyn, but I hadn't realized until recently you could walk from the island of Manhattan to the Bronx via the Henry Hudson Bridge.
I started from the northern side of Inwood Park, meaning I had to wind around to end up where the entrance to the bridge is. The bridge itself isn't inspiring to walk on, as the pedestrian walkway is on the lower level. However, it is on the western side, so there are expansive views of the Hudson and Harlem Rivers. During my crossing, the Metro-North bridge below me pivoted open to allow a local cruise ship through.
Rather than turning back, I decided to explore the area and then walk east to the 1 train. The neighborhood under the bridge has a small park, some actual single-family homes, and a Metro-North station. The riverfront here is taken up with railroad track; that plus the bridge makes for a slightly noisy neighborhood, but the houses feel surprisingly tranquil (and are even more surprisingly affordable. I mean, relatively. For New York.).
From there, I realized, I could walk back to Manhattan another way, by walking to Marble Hill. Geographically it's part of the Bronx, but jurisdictionally it's part of Manhattan, because it used to be part of it geographically. (Perfectly clear?) From Marble Hill the Broadway Bridge crosses over to the island of Manhattan, and I didn't realize it was a pedestrian bridge as well. It's actually a much easier way to cross over - except that technically both ends are in Manhattan!