Seattle's high-rises get a lot of love, but it also has some pretty decent mid-rise density in its inner neighborhoods around Downtown, as this photo shows. It's not quite San Francisco but still one of the more impressive urban landscapes west of the Mississippi. And even though the technology is light rail (not heavy rail), they have an underground subway that goes through several dense parts of the city, and are doing a massive expansion of grade-separated rail including a second tunnel through Downtown that will hit several additional inner and outer neighborhoods.